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Black phosphorus quantum dot-based field-effect transistors with ambipolar characteristics
Seo, Soonjoo,Park, Byoungnam,Kim, Youngjun,Lee, Hyun Uk,Kim, Hyeran,Lee, Seung Youb,Kim, Yooseok,Won, Jonghan,Kim, Youn Jung,Lee, Jouhahn Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.448 No.-
<P><B>Abstract</B></P> <P>Semiconductor quantum dots have intriguing electronic and optical properties distinguished from bulk owing to quantum confinement effects. Among the two-dimensional materials, black phosphorus (BP) has generated enormous excitement due to its tunable direct band gap and high p-type semiconducting properties. We prepared BP quantum dots (BPQDs) by simple liquid exfoliation using distilled water and ethanol solution. Our structural data show the uniform distribution of circular BPQDs with the average lateral size of 4.08 ± 0.66 nm and the height of 1.13 ± 0.32 nm. We fabricated BPQD field-effect transistors (FETs) to investigate the electrical characteristics of BPQD-based devices and found that both hole and electron transport can be probed in the BPQD FETs. The BPQD FETs exhibited unprecedentedly ambipolar behavior with the mobility of 0.11 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> for p type and 0.09 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> for n type at 300 K. Our results provide the simple preparation methods to fabricate ambipolar BPQD FETs with the comparable hole and electron transport for large-area applications in solar cells and optoelectronic devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The BPQDs can be mass-produced at room temperature. </LI> <LI> The BPQDs have the lateral size of ∼4.0 nm and the height of ∼1 nm. </LI> <LI> The BPQDs FETs exhibits ambipolar behavior with the comparable hole and electron mobility. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>BP quantum dot-based field effect transistor and its characteristic behavior.</P> <P>[DISPLAY OMISSION]</P>
Beom-sik Kim,Hee Jae Kang,Soonjoo Seo,Nam Seok Park 한국진공학회(ASCT) 2016 Applied Science and Convergence Technology Vol.25 No.2
The structural and the electronic properties of pentacene on modified Si (001) were investigated using scanning tunneling microscopy (STM), atomic force microscopy (AFM) and ultraviolet photoelectron spectroscopy (UPS). Dodecane was used to modify Si (001) substrates and then pentacene was deposited on dodecane/Si (001). Our STM results show a uniform distribution of aggregated dodecane molecules all over the clean Si (001). The surface structure of pentacene on dodecaene/Si (001) examined by AFM is analogous to that of pentacene on SiO2. The UPS data showed that the work function of pentacene on clean Si (001) and pentacene on modified Si (001) with dodecane was 6.41 and 5.57 eV, respectively. Our results prove that dodecane results in the work function difference between pentacene on clean Si (001) and pentacene on dodecane/Si (001).
Reflection electron energy loss spectroscopy for ultrathin gate oxide materials
Shin, Hye Chung,Tahir, Dahlang,Seo, Soonjoo,Denny, Yus Rama,Oh, Suhk Kun,Kang, Hee Jae,Heo, Sung,Chung, Jae Gwan,Lee, Jae Cheol,Tougaard, Sven Heyden & Son 2012 Surface and interface analysis Vol.44 No.6
<P>The band alignment of HfZrO<SUB>4</SUB> gate oxide thin films on Si (100) deposited by the atomic layer deposition method has been investigated using reflection electron energy loss spectroscopy and XPS. The band gap of HfZrO<SUB>4</SUB> gate oxide thin film is 5.40 ± 0.05 eV. The valence band offset (Δ<I>E</I><SUB>v</SUB>) and the conduction band offset (Δ<I>E</I><SUB>c</SUB>) are 2.50 ± 0.05 eV and 1.78 ± 0.05 eV, respectively. These values satisfy the minimum requirement for the hole and electron barrier heights of larger than 1 eV for device applications. We have demonstrated that the quantitative analysis of reflection electron energy loss spectroscopy spectra obtained from HfZrO<SUB>4</SUB> thin films provides us a straightforward way to determine the optical properties and the inelastic mean free path of ultrathin gate oxide materials. Copyright © 2012 John Wiley & Sons, Ltd.</P>
Kim, Beom-sik,Kang, Hee Jae,Seo, Soonjoo,Park, Nam Seok The Korean Vacuum Society 2016 Applied Science and Convergence Technology Vol.25 No.2
The structural and the electronic properties of pentacene on modified Si (001) were investigated using scanning tunneling microscopy (STM), atomic force microscopy (AFM) and ultraviolet photoelectron spectroscopy (UPS). Dodecane was used to modify Si (001) substrates and then pentacene was deposited on dodecane/Si (001). Our STM results show a uniform distribution of aggregated dodecane molecules all over the clean Si (001). The surface structure of pentacene on dodecaene/Si (001) examined by AFM is analogous to that of pentacene on $SiO_2$. The UPS data showed that the work function of pentacene on clean Si (001) and pentacene on modified Si (001) with dodecane was 6.41 and 5.57 eV, respectively. Our results prove that dodecane results in the work function difference between pentacene on clean Si (001) and pentacene on dodecane/Si (001).
Kim, Youngjun,Cho, Seongeun,Kim, Hyeran,Seo, Soonjoo,Lee, Hyun Uk,Lee, Jouhahn,Ko, Hyungduk,Chang, Mincheol,Park, Byoungnam Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.36
<P>Electric field-induced charge trapping and exciton dissociation were demonstrated at a penatcene/grapheme quantum dot (GQD) interface using a bottom contact bi-layer field effect transistor (FET) as an electrical nano-probe. Large threshold voltage shift in a pentacene/GQD FET in the dark arises from field-induced carrier trapping in the GQD layer or GQD-induced trap states at the pentacene/GQD interface. As the gate electric field increases, hysteresis characterized by the threshold voltage shift depending on the direction of the gate voltage scan becomes stronger due to carrier trapping associated with the presence of a GQD layer. Upon illumination, exciton dissociation and gate electric field-induced charge trapping simultaneously contribute to increase the threshold voltage window, which can potentially be exploited for photoelectric memory and/or photovoltaic devices through interface engineering.</P>
Non-ablative Fractional Thulium Laser Irradiation Suppresses Early Tumor Growth
Yoo, Su Woong,Park, Hee-Jin,Oh, Gyungseok,Hwang, Soonjoo,Yun, Misun,Wang, Taejun,Seo, Young-Seok,Min, Jung-Joon,Kim, Ki Hean,Kim, Eung-Sam,Kim, Young L.,Chung, Euiheon Optical Society of Korea 2017 Current Optics and Photonics Vol.1 No.1
In addition to its typical use for skin rejuvenation, fractional laser irradiation of early cancerous lesions may reduce the risk of tumor development as a byproduct of wound healing in the stroma after the controlled injury. While fractional ablative lasers are commonly used for cosmetic/aesthetic purposes (e.g., photorejuvenation, hair removal, and scar reduction), we propose a novel use of such laser treatments as a stromal treatment to delay tumorigenesis and suppress carcinogenesis. In this study, we found that non-ablative fractional laser (NAFL) irradiation may have a possible suppressive effect on early tumor growth in syngeneic mouse tumor models. We included two syngeneic mouse tumor models in irradiation groups and control groups. In the irradiation group, a thulium fiber based NAFL at 1927 nm was used to irradiate the skin area including the tumor injection region with 70 mJ/spot, while no laser irradiation was applied to the control group. Numerical simulation with the same experimental condition showed that thermal damage was confined only to the irradiation spots, sparing the adjacent tissue area. The irradiation groups of both tumor models showed smaller tumor volumes than the control group at an early tumor growth stage. We also detected elevated inflammatory cytokine levels a day after the NAFL irradiation. NAFL treatment of the stromal tissue could potentially be an alternative anticancer therapeutic modality for early tumorigenesis in a minimally invasive manner.