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RISS 인기검색어
- 검색키워드
- 저자 : Kwak Iljo (검색결과 2 건)
- 무료
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- 유료
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Band Structure Engineering of Layered WSe<sub>2</sub><i>via</i> One-Step Chemical Functionalization
Park, Jun Hong,Rai, Amritesh,Hwang, Jeongwoon,Zhang, Chenxi,Kwak, Iljo,Wolf, Steven F.,Vishwanath, Suresh,Liu, Xinyu,Dobrowolska, Malgorzata,Furdyna, Jacek,Xing, Huili Grace,Cho, Kyeongjae,Banerjee, S American Chemical Society 2019 ACS NANO Vol.13 No.7
<P>Chemical functionalization is demonstrated to enhance the p-type electrical performance of two-dimensional (2D) layered tungsten diselenide (WSe<SUB>2</SUB>) field-effect transistors (FETs) using a one-step dipping process in an aqueous solution of ammonium sulfide [(NH<SUB>4</SUB>)<SUB>2</SUB>S(aq)]. Molecularly resolved scanning tunneling microscopy and spectroscopy reveal that molecular adsorption on a monolayer WSe<SUB>2</SUB> surface induces a reduction of the electronic band gap from 2.1 to 1.1 eV and a Fermi level shift toward the WSe<SUB>2</SUB> valence band edge (VBE), consistent with an increase in the density of positive charge carriers. The mechanism of electronic transformation of WSe<SUB>2</SUB> by (NH<SUB>4</SUB>)<SUB>2</SUB>S(aq) chemical treatment is elucidated using density functional theory calculations which reveal that molecular “SH” adsorption on the WSe<SUB>2</SUB> surface introduces additional in-gap states near the VBE, thereby, inducing a Fermi level shift toward the VBE along with a reduction in the electronic band gap. As a result of the (NH<SUB>4</SUB>)<SUB>2</SUB>S(aq) chemical treatment, the p-branch ON-currents (<I>I</I><SUB>ON</SUB>) of back-gated few-layer ambipolar WSe<SUB>2</SUB> FETs are enhanced by about 2 orders of magnitude, and a ∼6× increase in the hole field-effect mobility is observed, the latter primarily resulting from the p-doping-induced narrowing of the Schottky barrier width leading to an enhanced hole injection at the WSe<SUB>2</SUB>/contact metal interface. This (NH<SUB>4</SUB>)<SUB>2</SUB>S(aq) chemical functionalization technique can serve as a model method to control the electronic band structure and enhance the performance of devices based on 2D layered transition-metal dichalcogenides.</P> [FIG OMISSION]</BR>
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Park, Jun Hong,Vishwanath, Suresh,Wolf, Steven,Zhang, Kehao,Kwak, Iljo,Edmonds, Mary,Breeden, Michael,Liu, Xinyu,Dobrowolska, Margaret,Furdyna, Jacek,Robinson, Joshua A.,Xing, Huili Grace,Kummel, Andr American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.34
<P>To fabricate practical devices based on semiconducting two-dimensional (2D) materials, the source, channel, and drain materials are exposed to ambient air. However, the response of layered 2D materials to air has not been fully elucidated at the molecular level. In the present report, the effects of air exposure on transition metal dichalcogenides (TMD) and metal dichalcogenides (MD) are studied using ultrahigh-vacuum scanning tunneling microscopy (STM). The effects of a 1-day ambient air exposure on MBE-grown WSe2, chemical vapor deposition (CVD)-grown MoS2, and MBE SnSe2 are compared. Both MBE grown WSe2 and CVD-grown MoS2 display a selective air exposure response at the step edges, consistent with oxidation on WSe2 and adsorption of hydrocarbon on MoS2, while the terraces and domain/grain boundaries of both TMDs are nearly inert to ambient air. Conversely, MBE-grown SnSe2, an MD, is not stable in ambient air. After exposure in ambient air for 1 day, the entire surface of SnSe2 is decomposed to SnOx and SeOx as seen with X-ray photoelectron spectroscopy. Since the oxidation enthalpy of all three materials is similar, the data is consistent with greater oxidation of SnSe2 being driven by the weak bonding of SnSe2.</P>
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