P417
886-2-2789-6711
wbsu [at] phys.sinica.edu.tw
P417
886-2-2789-6711
wbsu [at] phys.sinica.edu.tw
Chu, Michelle / 886-2-2789-8364
(1) | 國內學術研究獎項 | 2013-01 | 中華民國物理學刊優良論文甲等獎 | |
(2) | 國內學術研究獎項 | 2011-06 | 中研院年輕學者研究著作獎 |
(1) | 西元年:2016 研究人員(中):蘇維彬、林俊良、鄭文源、呂欣明、張嘉升 研究人員(英):SU, WEI-BIN, Chun-Liang Lin, Wen-Yuan Chan, Shin-Ming Lu, and Chia-Seng Chang 研究成果名稱(中):顯現於掃描穿隧顯術中的場發射共振的場增強因子與自我聚焦功能 研究成果名稱(英):Field enhancement factors and self-focus functions manifesting in field emission resonances in scanning tunneling microscopy 簡要記述(中):我們發現掃描穿隧顯微術中的場發射共振中存在著場增強因子與自我聚焦功能等兩種物理現象。前者影響場發射共振的數目,增強因子愈高,共振的數目會愈多。後者則使掃描穿隧顯微術中的探針在遠離表面時依然可使影像保有奈米的空間解析度,可成為奈米尺度的顯影技術。 簡要記述(英):Field emission (FE) resonance (or Gundlach oscillation) in scanning tunneling microscopy (STM) is a phenomenon in which the FE electrons emitted from the microscope tip couple into the quantized standing-wave states within the STM tunneling gap. Although the occurrence of FE resonance peaks can be semi-quantitatively described using the triangular potential well model, it cannot explain the experimental observation that the number of resonance peaks may change under the same emission current. This study demonstrates that the aforementioned variation can be adequately explained by introducing a field enhancement factor that is related to the local electric field at the tip apex. The peak number of FE resonances increases with the field enhancement factor. The peak intensity of the FE resonance on the reconstructed Au(111) surface varies in the face-center cubic, hexagonal-close-packed, and ridge regions, thus providing the contrast in the mapping through FE resonances. The mapping contrast is demonstrated to be nearly independent of the tip-sample distance, implying that the FE electron beam is not divergent because of a self-focus function intrinsically involved in the STM configuration.
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(2) | 西元年:2014 研究人員(中):蘇維彬 研究人員(英):SU, WEI-BIN 研究成果名稱(中):利用微米尺度探針增強的拉曼散射估計石墨烯之楊氏模數 研究成果名稱(英):Estimating Young’s modulus of graphene with Raman scattering enhanced by micrometer tip 簡要記述(中):我們利用懸浮石墨烯研究探針增強拉曼散射。我們發現石墨烯的拉曼訊號可以被微米尺寸的金探針針尖所增強,這與一般認為探針增強拉曼散射只會由奈米尺寸的針尖所引發不同。我們在探針上外加電壓並利用探針增強拉曼散射,可觀察到懸浮石墨烯因靜電力的吸引而產生形變。從形變的量測可進而估計石墨烯的楊氏模數。 簡要記述(英):We demonstrate that the Raman intensities of G and 2D bands of a suspended graphene can be enhanced using a gold tip with an apex size of 2.3 μm. The enhancement decays with the tip-graphene distance exponentially and remains detectable at a distance of 1.5 μm. Raman mappings show that the enhanced area is comparable to the apex size. Application of a bias voltage to the tip can attract the graphene so that Raman signals are intensified. The exponential enhancement-distance relationship enables the measurement of the graphene deformation, and the Young’s modulus of graphene is estimated to be 1.48 TPa.
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(3) | 西元年:2012 研究人員(中):蘇維彬、鄭文源、黃旭昇、林偉翔、鄭弘泰、吳茂昆、張嘉升 研究人員(英):SU, WEI-BIN, W. Y. Chan, H. S. Huang, W. H. Lin, H.-T. Jeng, M. K. Wu, and C. S. Chang 研究成果名稱(中):強電場引發的金屬薄膜膨脹效應 研究成果名稱(英):Field-induced expansion deformation effect in metallic films 簡要記述(中):我們利用超高真空低溫掃描穿隧顯微儀與能譜術,觀察在強電場作用下金屬薄膜中量子井能態的能量偏移。隨著電場強度的增加,我們發現大部分的量子井能態會顯現兩種能量偏移模式。第一種是單純的往高能量移動的偏移模式,第二種則是先往低能量再往高能量的偏移模式。此外我們也發現較高能量的量子井能態傾向顯現第一種模式,但隨著薄膜厚度的增加,會逐漸變成顯現第二種模式。這種厚度相依的現象反映表面原子會因電場作用而向外位移,進而帶動薄膜中原子的移動而產生膨脹效應,並且膨脹量會與薄膜厚度成正比。此發現開啟了在奈米尺度下利用量子井能態量測金屬薄膜的楊氏係數的可行性。研究成果論文已發表在《物理評論通訊》(Physical Review Letters 108, 146102 (2012) )。 簡要記述(英):We use low-temperature ultra high vacuum uses scanning tunneling microscopy and spectroscopy to observe the energy shift of quantum well states in metallic film under strong electric field. It is found that, with an increase of the electric field, the behavior of the energy shift can be grouped into two different modes for most QW states. In the first mode, the state energy moves toward high energy monotonically. In the second mode, the state energy shifts to a lower energy initially and then turns around to a higher energy. Moreover, we have observed that the QW states of higher energy behave in preference to the first mode, but they gradually change to the second mode as the Pb island becomes thicker. By measuring the energy shift at different electric field, This thickness-dpendent behavior reflects that the surface atoms can be displaced outward by the electric field, which can subsequently induce the movement of atoms in the film to establish an expansion deformation. It is also observed that the expansion is proportional to the film thickness. This finding opens up a possibility to measure the Young’s modulus of metallic film in the nano-meter scale. The paper has been published in Physical Review Letters 108, 146102 (2012)
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(4) | 西元年:2009 研究人員(中):蘇維彬、楊敏麒,林俊良,張嘉升,鄭天佐 研究人員(英):SU, WEI-BIN, M. C. Yang, C. L. Lin, C. S. Chang, T. T. Tsong 研究成果名稱(中):鏡像位能對成長於銅(111)面鉛島中未填滿量子井態的相位貢獻之研究 研究成果名稱(英):Phase Contribution of Image Potential on Empty Quantum Well States in Pb Islands on the Cu(111) Surface 簡要記述(中):先前利用掃描穿隧顯微術(STM)觀察金屬薄膜中量子井態的研究,都關注在費米能階附近+-2 eV能量範圍的量子井態。這些先前的研究顯示利用量子力學中的方形位能井模型可以清楚了解這能量範圍的量子井態。我們利用STM中的Z-V能譜術觀察鉛薄膜中於費米能階以上2-5 eV的未填滿量子井態。我們發現在這能量範圍的量子井態的能階會受到鏡像位能的影響,造成量子井態無法單純用方形位能井解釋。我們利用相位累積模型並在模型中引進鏡像位能的相位,成功解釋較高能量的量子井態的行為。此外,我們從相位累積模型的結果得到一有趣且重要的結論:在鉛薄膜外會存在一量子區域,鏡像位能在此區域會消失。由於這量子區域,當電子在金屬表面時,鏡像位能才不會發散成無窮大。此成果已發表在Physical Review Letters 102, 196102 (2009)。 簡要記述(英):Previous studies on the quantum-well (QW) states in metal films by using scanning tunneling microscopy (STM) focused on the QW states appearing in the energy range of +-2 eV around the Fermi level. These studies have shown that QW states in this energy range can be well described by the model of the square potential well in quantum mechanics. We use Z-V spectroscopy in STM to study the empty QW states of higher energies that are in the range of 2-5 eV above Fermi level for the Pb/Cu(111) system. Our observation shows that the QW states in this energy range significantly deviated from the description of square potential well. We introduce a phase factor contributed by the image potential in the phase accumulation (PA) model to calculate the energy levels of higher energy QW states. The calculated results are in good agreement with the experimental measurement, revealing that the higher energy empty QW states are indeed influenced by the image potential. Moreover, based on the PA model, we obtain an interesting and important point of view that there exists a quantum regime above the Pb surface in which the image potential is vanished. Owing to this quantum regime, the image potential will not become the infinity when the electron is at the metal surface. This paper has been published in Physical Review Letters 102, 196102 (2009).
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(5) | 西元年:2007 研究人員(中):蘇維彬、林俊良、呂欣明、張嘉升、鄭天佐 研究人員(英):SU, WEI-BIN, C. L. Lin, S. M. Lu, C. S. Chang, T. T. Tsong 研究成果名稱(中):功函數差異於高階昆拉赫振盪峰之呈現 研究成果名稱(英):Manifestation of Work Function Difference in High Order Gundlach Oscillation 簡要記述(中):當金屬薄膜的厚度在奈米的尺度時,薄膜的電性結構會受到量子尺寸效應的影響,進而使金屬薄膜的功函數隨厚度而變化。此課題在奈米科學上有其重要性,因為人們可以藉由量測功函數進而理解薄膜的電性結構。功函數是金屬中的電子要離開金屬所需克服的能量,一般可以利用光電子能譜量測。然而此技術是以光激發出電子,所用光源會涵蓋整個薄膜,因此薄膜的厚度必須要均勻,否則所量測的結果是多種厚度的功函數的平均值。所以薄膜的成長必須要是一層接一層的模式,才適合用光電子能譜,然而有很多薄膜系統的成長是不均勻的。為了克服這個限制,可以利用局部探測技術如掃描穿隧顯微儀,此技術不需要薄膜是均勻的成長。人們可以利用掃描穿隧顯微儀量測電子穿隧所面對的位能障礙,此物理量會與功函數相關。然而利用此方法量測的功函數的誤差高達0.3電子伏特,其精確度遠低於光電子能譜。 我們發現利用掃描穿隧顯微儀中的高階昆拉赫振盪的尖峰特徵可以對金屬薄膜的功函數作精確量測,其誤差可低於0.02電子伏特,精確度直逼光電子能譜。由於這是一技術上的突破,所以此成果發表在物理評論通訊(Phys. Rev. Lett. 99, 216103, (2007))。由於此技術具有高精確度,因此可以量測出某些奈米結構的功函數的微細差異,進而理解奈米結構不同的電性以及其中的物理,因此我們的發現為奈米科學的研究提供了新的方法。 簡要記述(英):When the thickness of a metal film is reduced to the nanometer size, its electronic structure will predominantly be governed by the quantum size effect, causing the work function to vary with the film thickness. This issue is of importance in nanoscience because one can realize the electronic structure of the thin film by measuring the work function. In general, one can measure the work function by using photoemission spectroscopy. However, owing to that it is a broad beam technique, it demands the metal film being grown in a layer-by-layer mode; otherwise what has been measured is just an average result over the films of various thicknesses. In order to overcome this limitation, a local probe technique such as scanning tunneling microscopy and spectroscopy (STM and STS) is an option without the need of a uniform film. Using STM, one can obtain the work function of the metal surface by measuring the apparent barrier height. Nevertheless, the general measured error with this method can be as high as 0.3 eV, much inferior to the precision achievable by the broad beam technique. We have found that the work function of the thin film can be precisely measured by using the Gundlach oscillation in STS. The precision of the measurement can be better than 0.02 eV, which is much better than that of detecting apparent barrier height with STM and is comparable to the photoemission results. This result has been published in Phys. Rev. Lett. 99, 216103, (2007). Since this technique has a high precision, one can use it to detect the subtle variation of the work function for some nanostructures. Therefore, Gundlach oscillation in STS can be a new way for the research of the nanoscience
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