Effect of Oxygen Adsorbates on Terahertz Emission Properties of Various Semiconductor Surfaces Covered with Graphene

Bagsican, Filchito Renee G.; Zhang, Xiang; Ma, Lulu; Wang, Minjie; Murakami, Hironaru; Vajtai, Róbert; Ajayan, Pulickel M.; Kono, Junichiro; Tonouchi, Masayoshi; Kawayama, Iwao

doi:10.1007/s10762-016-0301-x

Cited by 11 publications

(7 citation statements)

References 16 publications

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“…4. 24,26 At low laser fluences, the linear relationships between the intensities and laser power agree with Eqs. (3), (4), and (10).…”

Section: 𝜕𝑥supporting

confidence: 75%

“…Figure 2 shows an example of THz emission waveforms from n-type and p-type InP wafers with carrier densities of around 5x10 18 cm -3 and 1x10 18 cm -3 , respectively. 24 The signs of the waveforms differ depending on carrier type. For doped semiconductors, 𝑉 𝐷 can be replaced by the surface potential (Schottky-Barrier (SB)), which is often measured using a Kelvin Force Microscope (KFM).…”

Section: A Thz Radiation By Surge Drift Currentmentioning

confidence: 99%

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Simplified formulas for the generation of terahertz waves from semiconductor surfaces excited with a femtosecond laser

Tonouchi

2020

Journal of Applied Physics

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We derive simple formulas to explain terahertz (THz) emission from semiconductor surfaces excited by a femtosecond (fs) laser. Femtosecond optical pulses with energies larger than the bandgap create photocarriers which travel and generate THz radiation, according to the time derivative of the photocurrent. By assuming that only electrons traveling in an ultrafast time scale, less than a few hundred fs, contribute to THz radiation, one can obtain simple expressions for the emission originating from the photocarrier drift accelerated with a built-in field or from the photocarrier diffusion. The emission amplitude of the former is in proportion with electron mobility, the Schottky-Barrier height, and the laser intensity and one of the latter with the laser intensity and diffusion coefficient squared. We also discuss the formula for emission from metal-insulator-semiconductor structures. The derived expressions are useful in understanding the THz emission properties observed by a laser THz emission microscope (LTEM), bringing LTEM into real applications in the field of semiconductor research and development.

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“…4. 24,26 At low laser fluences, the linear relationships between the intensities and laser power agree with Eqs. (3), (4), and (10).…”

Section: 𝜕𝑥supporting

confidence: 75%

Section: A Thz Radiation By Surge Drift Currentmentioning

confidence: 99%

Simplified formulas for the generation of terahertz waves from semiconductor surfaces excited with a femtosecond laser

Tonouchi

2020

Journal of Applied Physics

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“…They observed that the THz radiation from graphene-coated InP is related to the adsorbed oxygen (O 2 ) induced localized electric dipoles, which further cause band structure modification in the surface depletion layer of InP [121]. While at graphene/InAs interface, O 2 adsorption/desorption showed negligible impact on the THz emission, which was mainly generated by transient diffusion photocurrent [122]. Moreover, they also realized the evaluation of adsorption energy of O 2 molecules on grapheneand WS 2 -based heterostructures due to thermal desorption [123].…”

Section: Interface Potential and Gas Adsorption/desorption Processes ...mentioning

confidence: 99%

Terahertz surface and interface emission spectroscopy for advanced materials

Huang

Yao

et al. 2019

J. Phys.: Condens. Matter

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Surfaces and interfaces are of particular importance for optoelectronic and photonic materials as they are involved in many physical and chemical processes such as carrier dynamics, charge transfer, chemical bonding, transformation reactions and so on. Terahertz (THz) emission spectroscopy provides a sensitive and nondestructive method for surface or interface analysis of advanced materials ranging from graphene to transition metal dichalcogenides, topological insulators, hybrid perovskites, and mixed-dimensional heterostructures based on 2D materials. In this review paper, we start with the THz radiation mechanisms under ultrafast laser excitation. Then we concentrate on the recent progresses of THz emission spectroscopy on the surface and interface properties of advanced materials, including transient surface photocurrents, surface nonlinear polarization, surface states, interface potential, and gas molecule adsorption/desorption processes. This novel spectroscopic method can not only promote the development of new and compact THz sources, but also provide a nondestructive optical method for surface and interface characterization of photocurrent and nonlinear polarization dynamics of materials.

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“…THz spectroscopy has been proven to be a powerful tool in studying the chemical and physical processes in a variety of systems 27 , 28 . In our work, we used the THz emission from the surface of InP coated with monolayer graphene to observe the relative concentration of O 2 adsorbates 29 , 30 . In this non-contact and non-destructive method, femtosecond infrared (IR) laser pulses are used to generate THz waves from a spot on the substrate surface.…”

Section: Introductionmentioning

confidence: 99%

Adsorption energy of oxygen molecules on graphene and two-dimensional tungsten disulfide

Bagsican

Winchester

Ghosh

et al. 2017

Sci Rep

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Adsorption of gas molecules on the surface of atomically layered two-dimensional (2D) materials, including graphene and transition metal dichalcogenides, can significantly affect their electrical and optical properties. Therefore, a microscopic and quantitative understanding of the mechanism and dynamics of molecular adsorption and desorption has to be achieved in order to advance device applications based on these materials. However, recent theoretical calculations have yielded contradictory results, particularly on the magnitude of the adsorption energy. Here, we have experimentally determined the adsorption energy of oxygen molecules on graphene and 2D tungsten disulfide using temperature-programmed terahertz (THz) emission microscopy (TPTEM). The temperature dependence of THz emission from InP surfaces covered with 2D materials reflects the change in oxygen concentration due to thermal desorption, which we used to estimate the adsorption energy of oxygen molecules on graphene (~0.15 eV) and tungsten disulphide (~0.24 eV). Furthermore, we used TPTEM to visualize relative changes in the spatial distribution of oxygen molecules on monolayer graphene during adsorption and desorption. Our results provide much insight into the mechanism of molecular adsorption on the surface of 2D materials, while introducing TPTEM as a novel and powerful tool for molecular surface science.The successful isolation of monolayer graphene in 2004 and its remarkable properties found subsequently have paved the way for a new research field of two-dimensional (2D) atomic layer materials [1][2][3][4] . Many other 2D materials have since been discovered with a wide range of characteristics, from metallic to semiconducting to insulating, opening up exciting new opportunities for the development of devices based on monolayers, bilayers, and heterostructures of 2D materials [5][6][7][8] . However, since these materials typically consist of one or a few atomic layers, their properties are extremely susceptible to perturbations from their environment. Exposure to gases, for example, has been shown to drastically affect their electrical and optical properties [9][10][11][12][13][14][15] , which means that in order to realize 2D-materials-based devices, it is crucial to understand and control the influence of gas adsorption and desorption dynamics on their properties.Of the possible gas adsorbates/contaminants, oxygen (O 2 ) is one of the most important because not only it significantly alters the properties through doping, it is also the second most abundant gas in the atmosphere and is therefore highly likely to affect the performance of devices in practical applications. Though theoretical simulations proved to be useful in understanding the interaction of O 2 molecules and/or O atoms with 2D materials, conflicting results for the adsorption energies were obtained due to the inability of the approximation functionals used to properly describe the dispersion forces [16][17][18][19][20][21][22][23] . Knowing the correct value of the adsorption ...

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Effect of Oxygen Adsorbates on Terahertz Emission Properties of Various Semiconductor Surfaces Covered with Graphene

Cited by 11 publications

References 16 publications

Simplified formulas for the generation of terahertz waves from semiconductor surfaces excited with a femtosecond laser

Simplified formulas for the generation of terahertz waves from semiconductor surfaces excited with a femtosecond laser

Terahertz surface and interface emission spectroscopy for advanced materials

Adsorption energy of oxygen molecules on graphene and two-dimensional tungsten disulfide

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