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RISS 인기검색어
- 검색키워드
- 저자 : DelRio, Frank W. (검색결과 3 건)
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Tran Khac, Bien-Cuong,DelRio, Frank W.,Chung, Koo-Hyun American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.10
<P>Surface damage characteristics of single- and multilayer hexagonal boron nitride (h-BN), molybdenum disulfide (MoS<SUB>2</SUB>), and graphene films were systematically investigated via atomic force microscopy (AFM)-based progressive-force and constant-force scratch tests and Raman spectroscopy. The film-to-substrate interfacial strengths of these atomically thin films were assessed based on their critical forces (i.e., the normal force where the atomically thin film was delaminated from the underlying substrate), as determined from progressive-force scratch tests. The evolution of surface damage with respect to normal force was further investigated using constant-force tests. The results showed that single-layer h-BN, MoS<SUB>2</SUB>, and graphene strongly adhere to the SiO<SUB>2</SUB> substrate, which significantly improves its tribological performance. Moreover, defect formation induced by scratch testing was found to affect the topography and friction force differently prior to failure, which points to distinct surface damage characteristics. Interestingly, the residual strains at scratched areas suggest that the scratch test-induced in-plane compressive strains were dominant over tensile strains, thereby leading to buckling in front of the scratching tip and eventually failure at sufficient strains. These trends represent the general failure mechanisms of atomically thin materials because of a scratch test. As the number of layers increased, the tribological performances of atomically thin h-BN, MoS<SUB>2</SUB>, and graphene were found to significantly improve because of an increase in the interfacial strengths and a decrease in the surface damage and friction force. In all, the findings on the distinctive surface damage characteristics and general failure mechanisms are useful for the design of reliable, protective and solid-lubricant coating layers based on these materials for nanoscale devices.</P> [FIG OMISSION]</BR>
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Surface Properties of Laser-Treated Molybdenum Disulfide Nanosheets for Optoelectronic Applications
Alrasheed, Abdullah,Gorham, Justin M.,Tran Khac, Bien Cuong,Alsaffar, Fadhel,DelRio, Frank W.,Chung, Koo-Hyun,Amer, Moh. R. American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.21
<P>Transition metal dichalcogenide two-dimensional materials have attracted significant attention due to their unique optical, mechanical, and electronic properties. For example, molybdenum disulfide (MoS<SUB>2</SUB>) exhibits a tunable band gap that strongly depends on the numbers of layers, which makes it an attractive material for optoelectronic applications. In addition, recent reports have shown that laser thinning can be used to engineer an MoS<SUB>2</SUB> monolayer with specific shapes and dimensions. Here, we study laser-thinned MoS<SUB>2</SUB> in both ambient and vacuum conditions via confocal μ-Raman spectroscopy, imaging X-ray photoelectron spectroscopy (i-XPS), and atomic force microscopy (AFM). For low laser powers in ambient environments, there is insufficient energy to oxidize MoS<SUB>2</SUB>, which leads to etching and redeposition of amorphous MoS<SUB>2</SUB> on the nanosheet as confirmed by AFM. At high powers in ambient, the laser energy and oxygen environment enable both MoS<SUB>2</SUB> nanoparticle formation and nanosheet oxidation as revealed in AFM and i-XPS. At comparable laser power densities in vacuum, MoS<SUB>2</SUB> oxidation is suppressed and the particle density is reduced as compared to ambient. The extent of nanoparticle formation and nanosheet oxidation in each of these regimes is found to be dependent on the number of layers and laser treatment time. Our results can shed some light on the underlying mechanism of which atomically thin MoS<SUB>2</SUB> nanosheets exhibit under high incident laser power for future optoelectronic applications.</P> [FIG OMISSION]</BR>
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Laser-Induced Particle Adsorption on Atomically Thin MoS<sub>2</sub>
Tran Khac, Bien Cuong,Jeon, Ki-Joon,Choi, Seung Tae,Kim, Yong Soo,DelRio, Frank W.,Chung, Koo-Hyun American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.5
<P>Atomically thin molybdenum disulfide (MoS2) shows great potential for use in nanodevices because of its remarkable electronic, optoelectronic, and mechanical properties. These material properties are often dependent on the thickness or the number of layers, and hence Raman spectroscopy is widely used to characterize the thickness of atomically thin MoS2 due to the sensitivity of the vibrational spectrum to thickness. However, the lasers used in Raman spectroscopy can increase the local surface temperature and eventually damage the upper layers of the MoS2, thereby changing the aforementioned material properties. In this work, the effects of lasers on the topography and material properties of atomically thin MoS2 were systematically investigated using Raman spectroscopy and atomic force microscopy. In detail, friction force microscopy was used to study the friction characteristics of atomically thin MoS2 as a function of laser powers from 0.5 to 20 mW and number of layers from 1 to 3. It was found that particles formed on the top surface of the atomically thin MoS2 due to laser-induced thermal effects. The degree of particle formation increased as the laser power increased, prior to the thinning of the atomically thin MoS2. In addition, the degree of particle formation increased as the number of MoS2 layers increased, which suggests that the thermal behavior of the supported MoS2 may differ depending on the number of layers. The particles likely originated from the atmosphere due to laser-induced heating, but could be eliminated via appropriate laser powers and exposure times, which were determined experimentally. The outcomes of this work indicate that thermal management is crucial in the design of reliable nanoscale devices based on atomically thin MoS2.</P>
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