Somphonsane, Ratchanok

Preferred name

Alternative Name

Somphonsane, R.

Main Affiliation

School of Science

ratchanok.so@kmitl.ac.th

Now showing 1 - 10 of 33

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Plasmon-mediated energy relaxation in graphene
(2015-12-28)
Ferry, D. K.
;
Somphonsane, R.
;
Ramamoorthy, H.
;
Bird, J. P.
Energy relaxation of hot carriers in graphene is studied at low temperatures, where the loss rate may differ significantly from that predicted for electron-phonon interactions. We show here that plasmons, important in the relaxation of energetic carriers in bulk semiconductors, can also provide a pathway for energy relaxation in transport experiments in graphene. We obtain a total loss rate to plasmons that results in energy relaxation times whose dependence on temperature and density closely matches that found experimentally.
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Signatures of hot carriers and hot phonons in the re-entrant metallic and semiconducting states of Moiré-gapped graphene
(2023-12-01)
Nathawat, Jubin
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Mansaray, Ishiaka
;
Sakanashi, Kohei
;
Wada, Naoto
;
Randle, Michael D.
Stacking of graphene with hexagonal boron nitride (h-BN) can dramatically modify its bands from their usual linear form, opening a series of narrow minigaps that are separated by wider minibands. While the resulting spectrum offers strong potential for use in functional (opto)electronic devices, a proper understanding of the dynamics of hot carriers in these bands is a prerequisite for such applications. In this work, we therefore apply a strategy of rapid electrical pulsing to drive carriers in graphene/h-BN heterostructures deep into the dissipative limit of strong electron-phonon coupling. By using electrical gating to move the chemical potential through the “Moiré bands”, we demonstrate a cyclical evolution between metallic and semiconducting states. This behavior is captured in a self-consistent model of non-equilibrium transport that considers the competition of electrically driven inter-band tunneling and hot-carrier scattering by strongly non-equilibrium phonons. Overall, our results demonstrate how a treatment of the dynamics of both hot carriers and hot phonons is essential to understanding the properties of functional graphene superlattices.
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Energy relaxation of hot carriers in graphene via plasmon interactions
(2016-03-01)
Ferry, D. K.
;
Somphonsane, R.
;
Ramamoorthy, H.
;
Bird, J. P.
Energy relaxation of hot carriers in graphene is studied theoretically and experimentally at low temperatures, where the loss rate may differ significantly from that predicted for electron–phonon interactions. We show here that plasmons, important in the relaxation of energetic carriers in bulk semiconductors, can also provide a pathway for energy relaxation in transport experiments in graphene. Reflecting the linear nature of graphene’s bands, we obtain a total loss rate to plasmons that is independent of carrier density. This results in energy relaxation times whose dependence on temperature and density closely matches that reported experimentally.
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Cost-Effective Experimental Setup for Studies of Spin Seebeck Effect and Electrical Transport in Thermoelectric Materials
(2020-06-01)
Wongjom, Poramed
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Thongsamrit, Wannisa
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Ramamoorthy, Harihara
;
Chinwong, Suriya
;
Somphonsane, Ratchanok
In this article, we report on the design of a low-cost, accurate, and easy-to-implement roomerature experimental setup to comprehensively study the spin Seebeck effect (SSE) in ferrimagnetic insulators (FIs). Neodymium permanent magnets (NdPMs) are used to generate a fixed uniform magnetic field while the sample is staged in a custom-designed vacuum chamber containing thermal baths (for generating the required temperature gradient) and a complete 360° sample rotation mechanism (for studying the magnetic field angle dependence). Our experiments reveal excellent magnetic field uniformity (±1%) formed between the magnet poles, a highly accurate temperature gradient stability (±1%), and excellent agreement of the longitudinal SSE (LSSE) response for the Pt/YIG structure studied here with those reported in the literature. We also measure the anomalous Nernst effect (ANE) exhibited in a graphite sample, demonstrating the capability of our setup to accurately measure this parameter. Finally, we demonstrate that our setup can also be used to measure the conventional Seebeck effect (SE) and the electrical resistivity of commercially obtained Bi<inf>2</inf>Te<inf>3</inf> samples, making it a versatile tool for the broad characterization of thermoelectric materials.
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Investigating the shunting effect in a Fe/Co ferromagnetic metal hybrid structure and its impact on the spin Seebeck effect
(2024-03-01)
Phumying, Santi
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Wongjom, Chalothon
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Pongophas, Ekkarat
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Infahsaeng, Yingyot
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Maiaugree, Wasan
The generation of spin voltage by heat, known as the spin Seebeck effect (SSE), involves the injection of spin current from a ferromagnetic to a normal metal. In this study, the shunting effect in SSE is investigated within a hybrid structure consisting of iron (Fe) and cobalt (Co) films deposited on a Si-wafer substrate using thermal evaporation [Si/Fe(500 nm)/Co(10 nm)]. Spin voltage measurements performed in the in-plane configuration revealed a voltage reversal in the Co film and Fe film. However, in the hybrid structure (Si/Fe/Co), the voltage signal exhibited consistent directionality. This intriguing observation hints at a potential shunting effect, wherein the voltage influence from the Fe layer contributes to the Co film. Consequently, it is deduced that a significant shunting effect occurs when the resistivity of Fe is approximately three orders of magnitude lower than that of the Co film. This insight sheds light on the intricate dynamics of spin thermoelectric applications, emphasizing the role of material properties in optimizing performance.
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Negative differential conductance & hot-carrier avalanching in monolayer WS2 FETs
(2017-12-01)
He, G.
;
Nathawat, J.
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Kwan, C. P.
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Ramamoorthy, H.
;
Somphonsane, R.
The high field phenomena of inter-valley transfer and avalanching breakdown have long been exploited in devices based on conventional semiconductors. In this Article, we demonstrate the manifestation of these effects in atomically-thin WS<inf>2</inf> field-effect transistors. The negative differential conductance exhibits all of the features familiar from discussions of this phenomenon in bulk semiconductors, including hysteresis in the transistor characteristics and increased noise that is indicative of travelling high-field domains. It is also found to be sensitive to thermal annealing, a result that we attribute to the influence of strain on the energy separation of the different valleys involved in hot-electron transfer. This idea is supported by the results of ensemble Monte Carlo simulations, which highlight the sensitivity of the negative differential conductance to the equilibrium populations of the different valleys. At high drain currents (>10 μA/μm) avalanching breakdown is also observed, and is attributed to trap-assisted inverse Auger scattering. This mechanism is not normally relevant in conventional semiconductors, but is possible in WS<inf>2</inf> due to the narrow width of its energy bands. The various results presented here suggest that WS<inf>2</inf> exhibits strong potential for use in hot-electron devices, including compact high-frequency sources and photonic detectors.
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Versatile Recognition of Graphene Layers from Optical Images Under Controlled Illumination Through Green-Channel Correlation Method
(2024-06-23)
Sahriar, Miah Abdullah
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Abed, Mohd Rakibul Hasan
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Somphonsane, Ratchanok
;
Jang, Houk
;
Nam, Chang Yong
The proposed method for identifying the number of exfoliated graphene layers on an oxide substrate from optical images is both simple and versatile. It involves using a limited number of input images for training, paired with a larger set of well-published Github images for testing and prediction. This study has employed a linear regression-based method in executing its thresholding process. This method leverages the red, green, and blue color channels of image pixels and establishes a correlation between the green channel of the background and the green channel of various graphene layers. The method is positioned as an alternative to both deep learning-based graphene recognition and traditional microscopic analysis. Notably, the proposed methodology performs well under conditions where the influence of surrounding light on the graphene-on-oxide sample is minimal. It enables the rapid identification of various graphene layers, showcasing its feasibility for non-destructive identification. The study also addresses the functionality of the methodology under nonhomogeneous lighting conditions, demonstrating successful predictions of graphene layers even in lower-quality images compared to those typically published in literature. In summary, the proposed methodology offers a quick, inexpensive, and effective means of non-destructively identifying graphene layers from optical images. Its versatility and performance under varying conditions make it a promising approach for practical applications in graphene research. Additionally, and critically: the methods highlighted in this research can be utilized across a multitude of disciplines (from bioengineering to electrical, materials, nanoengineering, etc.) for one of the most fundamental areas of experimental research in STEM at the undergraduate level: accurately identifying multiple systems from optical images. A broad, relevant, and timely curriculum can be built around data analytics and application to solving STEM problems - including components such as data mining, cleaning, wrangling, and analysis, and critically, tying in these processes in solving real experimental challenges in a laboratory setting.
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"freeing" Graphene from Its Substrate: Observing Intrinsic Velocity Saturation with Rapid Electrical Pulsing
(2016-01-13)
Ramamoorthy, H.
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Somphonsane, R.
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Radice, J.
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He, G.
;
Kwan, C. P.
Rapid (nanosecond-scale) electrical pulsing is used to study drift-velocity saturation in graphene field-effect devices. In these experiments, high-field pulses are utilized to drive graphene"s carriers on time scales much faster than that on which energy loss to the underlying substrate can occur, thereby allowing the observation of the highest saturation velocities reported to date. In a dramatic departure from the behavior exhibited by conventional metals and semiconductors, as the electron or hole density is reduced toward the charge-neutrality point, the drift velocity is found to reach values comparable to the Fermi velocity itself. Corresponding current densities are as large as 10<sup>9</sup> A/cm<sup>2</sup>, similar to the values reported for carbon nanotubes and for graphene-on-diamond transistors. In essence, our approach of rapid pulsing allows us to "free" graphene from the deleterious influence of its substrate, revealing a pathway to achieve the superior electrical performance promised by this material. The usefulness of this approach is not merely limited to graphene but should extend also to a broad variety of two-dimensional semiconductors.
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Remote Mesoscopic Signatures of Induced Magnetic Texture in Graphene
(2021-02-25)
Arabchigavkani, N.
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Somphonsane, R.
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Ramamoorthy, H.
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He, G.
;
Nathawat, J.
Mesoscopic conductance fluctuations are a ubiquitous signature of phase-coherent transport in small conductors, exhibiting universal character independent of system details. In this Letter, however, we demonstrate a pronounced breakdown of this universality, due to the interplay of local and remote phenomena in transport. Our experiments are performed in a graphene-based interaction-detection geometry, in which an artificial magnetic texture is induced in the graphene layer by covering a portion of it with a micromagnet. When probing conduction at some distance from this region, the strong influence of remote factors is manifested through the appearance of giant conductance fluctuations, with amplitude much larger than e2/h. This violation of one of the fundamental tenets of mesoscopic physics dramatically demonstrates how local considerations can be overwhelmed by remote signatures in phase-coherent conductors.
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Conduction Mechanisms in CVD-Grown Monolayer MoS2 Transistors: From Variable-Range Hopping to Velocity Saturation
(2015-08-12)
He, G.
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Ghosh, K.
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Singisetti, U.
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Ramamoorthy, H.
;
Somphonsane, R.
We fabricate transistors from chemical vapor deposition-grown monolayer MoS<inf>2</inf> crystals and demonstrate excellent current saturation at large drain voltages (V<inf>d</inf>). The low-field characteristics of these devices indicate that the electron mobility is likely limited by scattering from charged impurities. The current-voltage characteristics exhibit variable range hopping at low V<inf>d</inf> and evidence of velocity saturation at higher V<inf>d</inf>. This work confirms the excellent potential of MoS<inf>2</inf> as a possible channel-replacement material and highlights the role of multiple transport phenomena in governing its transistor action.

Somphonsane, Ratchanok

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