Houk Jang

Harvard University

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Jong‐Hyun Ahn

Yonsei University

Takashi Taniguchi

National Institute for Materials Science

Suji Park

SLAC National Accelerator Laboratory

Donhee Ham

Harvard University

You Zhou

Harvard University

Henry Hinton

Harvard University

Kenji Watanabe

National Institute for Materials Science

Xiang Chen

Nanjing University of Science and Technology

Ruihao Ni

University of Maryland, College Park

Tanmoy Das

Saveetha University

Cooperative Institutions

Government of the Republic of Korea

Yonsei University

Samsung (South Korea)

Sungkyunkwan University

Seoul National University

Institute for Basic Science

Korea Institute of Science and Technology

Korea Advanced Institute of Science and Technology

Korea University

Pohang University of Science and Technology

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Carrier Dynamics: Transient SHG Imaging on Ultrafast Carrier Dynamics of MoS₂ Nanosheets (Adv. Mater. 14/2018)

Advanced Materials (2018)

Houk Jang Krishna P. Dhakal Kyung‐Il Joo Won Seok Yun Sachin M. Shinde

In article number 1705190, Jong-Hyun Ahn, and Hyunmin Kim, and co-workers report the generation of acoustic phonons triggered by an A-excitonic resonance in atomically thin molybdenum sulfide (MoS2) crystals with a sub-micrometer lateral optical resolution using time-resolved second-harmonic generation (SHG) microscopy. This approach may pave the way toward new sensing applications involving light-induced acoustic phonons in a wide variety of materials and structures with different interfacial carrier dynamics at play.

10.1002/adma.201870099

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Excitation-Dependent High-Lying Excitonic Exchange via Interlayer Energy Transfer from Lower-to-Higher Bandgap 2D Material

Nano Letters (2023)

Arka Karmakar T. Kazimierczuk Igor Antoniazzi Mateusz Raczyński Suji Park

High light absorption (∼15%) and strong photoluminescence (PL) emission in monolayer (1L) transition metal dichalcogenides (TMDs) make them ideal candidates for optoelectronic device applications. Competing interlayer charge transfer (CT) and energy transfer (ET) processes control the photocarrier relaxation pathways in TMD heterostructures (HSs). In TMDs, long-distance ET can survive up to several tens of nm, unlike the CT process. Our experiment shows that an efficient ET occurs from the 1Ls WSe2-to-MoS2 with an interlayer hexagonal boron nitride (hBN), due to the resonant overlapping of the high-lying excitonic states between the two TMDs, resulting in enhanced HS MoS2 PL emission. This type of unconventional ET from the lower-to-higher optical bandgap material is not typical in the TMD HSs. With increasing temperature, the ET process becomes weaker due to the increased electron-phonon scattering, destroying the enhanced MoS2 emission. Our work provides new insight into the long-distance ET process and its effect on the photocarrier relaxation pathways.

10.1021/acs.nanolett.3c01127

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Citations (8)

Wafer-Scale Synthesis and Transfer of Graphene Films

Nano Letters (2010)

Youngbin Lee Sukang Bae Houk Jang Sukjae Jang Shou-En Zhu

We developed means to produce wafer scale, high-quality graphene films as large as 3 inch wafer size on Ni and Cu films under ambient-pressure and transfer them onto arbitrary substrates through instantaneous etching of metal layers. We also demonstrated the applications of the large-area graphene films for the batch fabrication of field-effect transistor (FET) arrays and stretchable strain gauges showing extraordinary performances. Transistors showed the hole and electron mobilities of the device of 1,100 cm2/Vs and 550 cm2/Vs at drain bias of -0.75V, respectively. The piezo-resistance gauge factor of strain sensor was ~6.1. These methods represent a significant step toward the realization of graphene devices in wafer scale as well as application in optoelectronics, flexible and stretchable electronics.

Gauge factor

Strain gauge

10.1021/nl903272n

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Citations (1,096)

Flexible Electronics: Highly Flexible Hybrid CMOS Inverter Based on Si Nanomembrane and Molybdenum Disulfide (Small 41/2016)

Small (2016)

Tanmoy Das Xiang Chen Houk Jang Il‐Kwon Oh Hyungjun Kim

On page 5720, J.-H. Ahn and co-workers demonstrate large area, flexible hybrid complementary metal–oxide–semiconductor (CMOS) logic inverter based on the combination of ultrathin p-channel c-Si nanomembranes and n-channel chemical vapor deposition MoS2 transistors. Such integration of high performance Si technology with transition-metal dichalcogenides offers reliable electrical and mechanical properties and promises a realistic path for the fabrication of flexible/transparent CMOS circuits in 2D electronics.

Molybdenum disulfide

Flexible Electronics

Nanoelectronics

10.1002/smll.201670211

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Sub-wavelength optical lattice in 2D materials

arXiv (Cornell University) (2024)

Supratik Sarkar Mahmoud Jalali Mehrabad D. G. Suárez-Forero Liuxin Gu Christopher J. Flower

Recently, light-matter interaction has been vastly expanded as a control tool for inducing and enhancing many emergent non-equilibrium phenomena. However, conventional schemes for exploring such light-induced phenomena rely on uniform and diffraction-limited free-space optics, which limits the spatial resolution and the efficiency of light-matter interaction. Here, we overcome these challenges using metasurface plasmon polaritons (MPPs) to form a sub-wavelength optical lattice. Specifically, we report a ``nonlocal" pump-probe scheme where MPPs are excited to induce a spatially modulated AC Stark shift for excitons in a monolayer of MoSe$_2$, several microns away from the illumination spot. Remarkably, we identify nearly two orders of magnitude reduction for the required modulation power compared to the free-space optical illumination counterpart. Moreover, we demonstrate a broadening of the excitons' linewidth as a robust signature of MPP-induced periodic sub-diffraction modulation. Our results open new avenues for exploring power-efficient light-induced lattice phenomena below the diffraction limit in active chip-compatible MPP architectures.

Lattice (music)

10.48550/arxiv.2406.00464

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High-Performance Flexible Graphene Field Effect Transistors with Ion Gel Gate Dielectrics

Nano Letters (2010)

Beom Joon Kim Houk Jang Seoung-Ki Lee Byung Hee Hong Jong‐Hyun Ahn

A high-performance low-voltage graphene field-effect transistor (FET) array was fabricated on a flexible polymer substrate using solution-processable, high-capacitance ion gel gate dielectrics. The high capacitance of the ion gel, which originated from the formation of an electric double layer under the application of a gate voltage, yielded a high on-current and low voltage operation below 3 V. The graphene FETs fabricated on the plastic substrates showed a hole and electron mobility of 203 +/- 57 and 91 +/- 50 cm(2)/(V x s), respectively, at a drain bias of -1 V. Moreover, ion gel gated graphene FETs on the plastic substrates exhibited remarkably good mechanical flexibility. This method represents a significant step in the application of graphene to flexible and stretchable electronics.

Electron Mobility

Flexible Electronics

10.1021/nl101559n

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Citations (411)

Flexible, transparent single-walled carbon nanotube transistors with graphene electrodes

Nanotechnology (2010)

Sukjae Jang Houk Jang Youngbin Lee Daewoo Suh Seunghyun Baik

This paper reports a mechanically flexible, transparent thin film transistor that uses graphene as a conducting electrode and single-walled carbon nanotubes (SWNTs) as a semiconducting channel. These SWNTs and graphene films were printed on flexible plastic substrates using a printing method. The resulting devices exhibited a mobility of ∼ 2 cm(2) V(-1) s -1), On/Off ratio of ∼ 10(2), transmittance of ∼ 81% and excellent mechanical bendability.

10.1088/0957-4484/21/42/425201

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Citations (79)

Optical Image Analysis of Wse2 - Thresholding for Layer Detection

Miah Abdullah Sahriar Abdul Hamid Rumman Ahammad Ullah Bappy K. Barua Shohaib Ibne Monju

10.2139/ssrn.5042213

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Transient SHG Imaging on Ultrafast Carrier Dynamics of MoS₂ Nanosheets

Advanced Materials (2018)

Houk Jang Krishna P. Dhakal Kyung‐Il Joo Won Seok Yun Sachin M. Shinde

Abstract Understanding the collaborative behaviors of the excitons and phonons that result from light–matter interactions is important for interpreting and optimizing the underlying fundamental physics at work in devices made from atomically thin materials. In this study, the generation of exciton‐coupled phonon vibration from molybdenum disulfide (MoS 2 ) nanosheets in a pre‐excitonic resonance condition is reported. A strong rise‐to‐decay profile for the transient second‐harmonic generation (TSHG) of the probe pulse is achieved by applying substantial (20%) beam polarization normal to the nanosheet plane, and tuning the wavelength of the pump beam to the absorption of the A‐exciton. The time‐dependent TSHG signals clearly exhibit acoustic phonon generation at vibration modes below 10 cm −1 (close to the Γ point) after the photoinduced energy is transferred from exciton to phonon in a nonradiative fashion. Interestingly, by observing the TSHG signal oscillation period from MoS 2 samples of varying thicknesses, the speed of the supersonic waves generated in the out‐of‐plane direction (Mach 8.6) is generated. Additionally, TSHG microscopy reveals critical information about the phase and amplitude of the acoustic phonons from different edge chiralities (armchair and zigzag) of the MoS 2 monolayers. This suggests that the technique could be used more broadly to study ultrafast physics and chemistry in low‐dimensional materials and their hybrids with ultrahigh fidelity.

Molybdenum disulfide

10.1002/adma.201705190

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Citations (27)

Large-scale pattern growth of graphene films for stretchable transparent electrodes

Nature (2009)

Keun‐Soo Kim Yüe Zhao Houk Jang Sangyoon Lee Jong Min Kim

Microscale chemistry

Graphene foam

10.1038/nature07719

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Citations (10,148)