1 Low Dimensional Science －－－－ 2012 Summer Workshop

1

Low Dimensional Science－ － － －

2012 Summer Workshop

主辦單位：中興大學 物理系／奈米所

協辦單位：彰化師範大學 物理系 東海大學 物理系

國科會 物理研究推動中心 中興大學 奈米中心

中興大學 理學院應用科技中心

中華民國 101 年 8 月 29 日~8 月 31 日

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Low Dimensional Science－ － －2012 Summer Workshop －

活動日期：101 年 8 月 29 日(星期三)~101 年 8 月 31 日(星期五) 活動地點：中興大學理學大樓 3A12 室

活動網址：http://140.120.11.1/LDS/index.htm 主辦單位：中興大學 物理系/奈米科學研究所

協辦單位：彰化師範大學 物理系、東海大學 物理系

中興大學 奈米中心、中興大學 理學院應用科技中心 國科會自然處物理研究推動中心

Program Committee： C. C. Su(蘇志川), J. H. Wu (伍健華) Secretary：C. C. Chen(陳佳君)

Coordinator：Y. W. Suen(孫允武)

8/29(三) 14:00 ~15:20 Chair:

蘇志川 Co Chair:

張嘉升

14:00~14:20

中興大學 伍健華

The mechanical properties of C

84

molecules embedded Si (111) substrate

14:20~14:40

中興大學 游明翰

A New Method to Prepare Nano-cluster Tips Applied to Scanning Kelvin Probe Microscopy

14:40~15:00

中興大學 邱政中

Properties of SnO

2

thin film gas sensor under UV-LED light irradiation at room temperature

15:00~15:20 中興大學 陳韋豪

Photoelectric and magnetic properties of Mn doped ZnO nanowires

15:30~16:00 Coffee Break

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16:00~17:50 Tutorial session Chair:

何孟書

16:00~16:40 台灣大學 林敏聰 教授

Low dimensional magnetism: Some recent examples in

perpendicular magnetization and spin-polarized scanning tunneling microscopy

16:40~17:20 中央研究院 張嘉升 研究員

Critical Capillary Absorption of Current-melting Silver Nanodroplets into Multiwall Carbon Nanotubes

17:20~17:50 中興大學 周哲甫

Adsorption and Dynamics behaves of Platinum Atoms on

Si(111)-7x7 Surface Studied with Scanning Tunneling Microscopy and First principles Calculation

18:00 Dinner

19:30~ 經驗意見交流

8/30(四)

9:00~10:00 Chair:

江丞偉 Co Chair:

林敏聰

9:00~9:20 中興大學 許文馨 Paper-Based ELISA

9:20~9:40 中興大學 黃品琇

Investigation of Mouse Fibroblast cells with TiO

2

nanoparticles

9:40~10:00 中興大學 黃重浩

Surface-acoustic wave radio frequency identification system- design for the tag

10:00~10:30 Coffee Break

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10:30~12:00 Tutorial session Chair:

郭華丞

10:30~11:10 中央研究院 陳啟東 研究員

Nanopore as a Platform for Devices Containing Nanoparticles and Stacked-Sheets

11:20~12:00 中央研究院 蘇維彬 研究員

Quantum confinement effect: its influence on the growth of metal films and applications

12:00 Lunch

13:30~15:30 Chair:

周哲甫 Co Chair:

陳啟東

13:30~14:00 嘉義大學 蘇炯武 教授

單光軸異向性引致表面磁光法拉第旋轉角的訊號震盪現象

14:00~14:30 彰化師大 趙建都

Current-induced magnetization switching of magnetic tunnel junctions

14:30~14:50 彰化師大 李彥琦

Extraordinary tunneling magnetoresistance by the mediation of iron nanoparticles embedded in the MgO based magnetic tunnel junction

14:50~15:10 彰化師大 郭政宜

Effect of direct current polarity on the magnetization reversal of high aspect ratio spin valve

15:10~15:30 中興大學 余彥模

Confocal microscope with long optical path under lower temperature

15:30~16:00 Coffee Break

16:00~18:00 Chair:

李國誌 Co Chair:

蘇維彬

16:00~16:30 彰化師大 陳浩軒

Dipolar Coupling Array of Perpendicular to Plane Polarizer Spin-Torque Nano-Oscillators with Any Number

16:30~16:50 彰化師大 楊婕妤

Study of the interaction between vortices and different composite arrays in

superconducting Nb film

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16:50~17:10 中興大學 許詩怡

FeSeTe superconductive thin film by sputter system

17:10~17:30 中興大學 張為淳

Properties of FeSeTe Microbridge fabricated by Focus Ion Beam

17:30~17:50 中興大學 吳函樺

The Microstructure and Electrical Properties of YBCO Microbridge with Variable Thickness Fabricated by Focused Ion Beam

18:00 Dinner

19:30~ 與專家會談

8/31(五)

9:00 ~12:00 Chair:

何孟書

合作計畫討論會

12:00 Lunch

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The electricoptical mechanical properties of C

84

中興大學 伍健華

molecules embedded Si (111) substrate

Kuo-You Huang (黃國佑), and Jian-Hua Wu (伍健華), Mon-Shu Ho (何孟書) Department of Physics, National Chung Hsing University, Taichung 402, Taiwan

＊

Abstract

Silicon carbide is one of the most important semiconduction materials with high hardness. But high density of defeat on its surface making it become difficult to fabricate nanodevice. To improve such defeat, in this study, we use fullerene molecules to replace carbon source in silicon carbide.

The fullerene molecules has been attracted considerable attention and studied extensively because of its special structure and properties. C₈₄ is one of fellerene family, composing of 84 carbon atoms, with elliptic shape. In this experiment, we evaporate the C₈₄

References

molecules and make them deposited on the Si(111)-7x7 surface by k-cell in ultra-high vacuum chamber. Topography was taken by ultra-high vacuum scanning tunneling microscopy (UHV-STM). To measure mechanical properties, we use ultra-high vacuum atomic force microscopy (UHV-AFM). In this study, we found that the C-Si bond enhance the hardness of the substrate

[1]. T.-H. Fang, J.-H. Wu/ Computational Materials Science 43 (2008) 785–790 [2]. APPLIED PHYSICS LETTERS 93, 171908 2008

[3]. 國立成功大學 機械工程學系碩士論文 分子動力學應用於薄膜機械性質之計量與實驗 劉政 良

[4]. Langmuir 2010, 26(6), 4480–4488

[5]. T.-H. Fang, J.-H. Wu/ Computational Materials Science 43 (2008) 785–790 [6]. Anthony C. Fischer-Cripps Introduction to contact mechanics (second edition)

A New Method to Prepare Nano-cluster Tips Applied to Scanning Kelvin Probe Microscopy

中興大學 游明翰

M.-H. Yu¹, M.-N. Chang¹, C.-T. Lin², M.-H. Shiao²

1Institute of Nanoscience, National Chung Hsing University, Taichung, Taiwan

2

Abstract

Instrument Technology Research Center, National Applied Research Laboratories, Hsinchu, Taiwan

In this work, we modified nano-cluster tips by electroless electroplate in order to improve the sensitivity of scanning Kelvin probe microscopy (SKPM). For a metallic nano-cluster at a tip apex, we employed an atomic force microscopy (AFM) system to deposit a silver nano-cluster at the AFM tip apex. Figure 1 shows the tip apex before and after electroless electroplate. The samples used in this study are surface silver nano particles on a silicon substrate. Experimental results indicated that the modified tips can be used to improve the image quality of scanning Kelvin probe microscopy (SKPM).

Fig. 1. Tip apex before (left) and after (right) modification.

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Properties of SnO

2

中興大學 邱政中

thin film gas sensor under UV-LED light irradiation at room temperature.

Cheng-Chung Chiu, Hung-Ju Lin and Chiu-Hsien

Department of Physics, National Chung Hsing University, Taichung 402, Taiwan Wu ,

Abstract The SnO₂

References

thin film as ozone gas sensor was deposited on glass substrate by RF magnetron sputtering. We find that the thin film deposited at 700 ℃ shows excellent performance to detect ozone by UV-LED irradiation. The property of sensor irradiated by UV-LED with different power was discussed in this work. We find the sensor response for ozone depends on LED power. The sensor cannot detect a very small concentration of ozone due to a small-power UV-LED.

[1] ZM Jarzebski and JP Marton, J. Electrochem. Soc., 123 (1976) 199C [2] C. Klein and CS HurlBut: Proc 1993"Manual ofMineralogy" P383

[3] M. Batzill,U. Diebold “The surface and materials science of tin oxide”, Progress in Surface Science 79 (2005) 47–154

[4 ] physicsweb

[5] D. Morita, M. Sano, M. Yamamoto, T. Murayama, S. Nagahama, and T. Mukai, “High output power 365 nm ultraviolet light emitting diode of GaN-free structure,” Jpn. J. Appl. Phys., vol. 41, pp.

L1434-L1436, 2002.

http://physicsweb.org/articles/news/10/5/10/1

[6] T. Sahm, A. Gurlo, N. Bârsan, U. Weimar,” Basics of oxygen and SnO2 interaction;”work function change and conductivity measurements” Sensors and Actuators B: Chemical, Volume 118, Issues 1–2, 25 October 2006, Pages 78-83

[7] Matthias Batzill *, Ulrike Diebold, "The surface and materials science of tin oxide," Progress in Surface Science 79 (2005) 47–154

[8] Z. M. Jarzebski, Physical Properties of SnO2 Materials, J. Electrochem. Society，(1976) 199C-205C.

[9] N. Yamazoe, J. Fuchigami, M. Kishikawa, T. Seiyama, "Interactions of tin oxide surface with O2, H2O AND H2", Surface Science, 86 (1979) 335-344.

Photoelectric and magnetic properties of Mn doped ZnO nanowires

中興大學 陳韋豪

W.-H. Chen(陳韋豪),Y.-C. Lin(林宥辰), C-C Su(蘇志川),P. S. Liu(劉邦軒),C. W. Tseng(曾紀維), M.-S. Ho(何孟書)

Department of Physics, National Chung Hsing University, Taichung 402, Taiwan

Abstract

In recent studies, the photosensitive properties of zinc oxide were wildly applied to fabricate various photoelectric devices, such as ultra-violent detectors, photosensitive field effect transistors, etc. In this presentation, we use ion implantation to dope manganese on zinc oxide nanowire to discuss their effect to photosensitive properties.

Zinc oxide nanowires and nanorods were grown by vapor-liquid-solid (VLS) method.The devices using single ZnO nanowire have been manufactured by focus ion beam (FIB). Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and other analyzing instruments were used to determine the material properties, as morphology, crystal structures, grown orientation, composition of zinc oxide nanowires and nanorods.

8

Probing Low Dimensional Magnetic Structure with Spin-Polarized Scanning Tunneling Microscopy

國立台灣大學 林敏聰 教授 Minn-Tsong Lin

Department of Physics, National Taiwan University, 10617 Taipei, Taiwan

*

Institute of Atomic and Molecular Sciences, Academia Sinica, 10617 Taipei, Taiwan

Abstract

In application of spin-polarized scanning tunneling microscopy (SP-STM), we investigated magnetic interaction in nanometer scale between triangular Co nano-islands formed in the sub-monolayer Co deposited on Cu(111) substrate. The SP-STM images the magnetization or the relative spin configuration of the Co islands. The results indicate a competition between exchange coupling and dipolar interaction in nanometer scale among the conjoint Co islands. The parallel magnetization of a set of conjoint Co nano-islands is anticipated due to the ferromagnetic exchange coupling. However, significant numbers of sets with anti-parallel ordering can still be observed. In order to explain the anti-parallel data, we calculate the dipolar interaction between conjoint Co islands to realize if it is comparable with the exchange coupling strength, which could be correlated to the length of contact region. As a result, the SP-STM images and the statistical data indicate a competition between the dipolar interaction and the exchange coupling in nanometer scale. The anti-parallel configuration, in which dipolar energy dominates, is shown to be limited by the contact length of two conjoint islands, which scales the strength of exchange coupling.

*email: mtlin@phys.ntu.edu.tw

Critical Capillary Absorption of Current-melting Silver Nanodroplets into Multiwall Carbon Nanotubes*

中央研究院 張嘉升 研究員 Yen-Song Chen, Yuan-Chih Chang,

Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan

Shau-Chieh Wang, Li-Ying Chen, Der-Hsien Lien, Lih-Juann Chen, and Chia-Seng Chang

Department of Physics, National Taiwan University, Taipei 10617, Taiwan

Department of Materials Science and Engineering, National Tsing-Hua University Hsinchu 30013, Taiwan

Abstract

According to a recent molecular dynamic simulation, a single wall carbon nanotube (SWCNT) with open end might act as a “capillary pipette”, which can absorb nonwetting metal nanoparticles.

This capillary phenomenon has been observed experimentally in nanodroplets of various transition metals encapsulated inside the CNTs. In our study, in situ observations of the capillary absorption of current-melting Ag nanodroplets by the tailored multiwall carbon nanotubes are presented. As the ratio (η) of a droplet’s size to a CNT’s inner diameter goes below a critical value, the nonwetting Ag droplet can be drawn into the hollow core of the CNT through the capillary action. We also discover the contact angle between a Ag droplet and a CNT inner wall increases when the inner diameter of the CNT gets smaller. This results in the dependence of the critical absorption value of ηc on the CNT’s inner diameter (D_t), i.e. ηc will rise monotonically with D_t

Reference

when it is less than ~8 nm, implying the capillarity at the nanometer scale also exhibits the size-dependent nature. [1]

[1] Yen-Song Chen, Yuan-Chih Chang,

*We thank the support from the National Nanoscience and Nanotechnology Program of Taiwan under the grant number of NSC97-2120-M-001-008.

Shau-Chieh Wang, Li-Ying Chen, Der-Hsien Lien, Lih-Juann Chen, and Chia-Seng Chang, Small 8, 2158 (2012).

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Adsorption and Dynamics behaves of Platinum Atoms on Si(111)-7x7 Surface Studied with Scanning Tunneling Microscopy and First principles Calculation

中興大學 周哲甫

Che-Fu Chou (周哲甫), Chou-MinYang (楊朝閔), Mon-Shu Ho (何孟書) Department of Physics, National Chung Hsing University, Taichung 402, Taiwan

Abstract

In this study, behaves of platinum atoms on Si (111) surface were study in use of ultrahigh vacuum scanning tunneling microscope (STM). The surface morphologies of platinum atoms adsorbed on Si (111) surface were observed. Dynamic study showed how the platinum atoms adsorbing and hopping on Si (111) surface. Activation energy was also calculated by fitting the experimental data. A first principle calculation was then performed to establish the adsorption sites, hopping path and the activation energy in the experiment.

Keywords: Si、Pt、STM、111、7x7、first principle

Paper-Based ELISA

中興大學 許文馨

Wen-Hsin Hsu¹, Mon-Shu Ho¹, Chao-Min Cheng² et al.

1 Institute of NanoScience, National Chung-Hsing University ,Taiwan

2

Abstract

Institute of NanoEngineering and Microsystems, National Tsing Hua University, Taiwan

ELISA is widely used in biochemical analyses; these assays are typically carried out in microtiter plates or small vials. ELISA combines the specificity of antibodies with high-turnover catalysis by enzymes to provide specificity and sensitivity. Conventional ELISA have some disadvantage: needing large amount of samples, expensive and slow in process. Therefore we developed a new method named as Paper-based ELISA (P-ELISA) which is more inexpensive and more rapidly. It’s fabricated by patterning hydrophobic polymer in hydrophilic paper—as a platform for biochemical analysis. We also established that P-ELISA can be used to detect and quantify antibodies to the HIV-1 envelope antigen gp41 in human serum using an anti-human IgG antibody conjugated to alkaline phosphatase (ALP) to produce a colorimetric readout. The R²

Reference

value of the curve fit to the data using the Hill Equation is 0.992. We believe that the combination of ELISA and patterned paper will provide a useful new protocol for performing immunoassays. P-ELISA thus extends the range of application of ELISA, especially to small laboratories, and to developing countries.

[1]. R. Edwards, Immunodiagnostics, Oxford University Press, Oxford, 1999.Cheng, C.M., et al., Angew Chem Int Ed Engl, 2010. 49, 4771 (2010).

[2]. E. P. Diamandis, Immunoassay, Academic Press, St.Louis, 1996.

[3]. A.W. Martinez, S. T. Phillips, M. J. Butte, G. M. Whitesides, Angew. Chem. 2007, 119, 1340 – 1342; Angew. Chem. Int. Ed. 2007, 46, 1318 – 1320.

Fig.1 The standard curve of rabbit IgG.

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Investigation of Mouse Fibroblast cells with TiO

2 中興大學 黃品琇

nanoparticles

Tz-Ju Hong, Pin-Siou Huang

Institute of NanoScience, National Chung-Hsing University ,Taiwan , Mon-Shu Ho

Abstract

Titanium dioxide (TiO₂) is an important industrial material that is widely used as an additive incosmetics, pharmaceuticals and food colorants. Although the small size of the TiO₂ nanoparticle is useful in various applications, the biosafety of this material needs to be assessed . In this study, mouse fibroblast (NIH 3T3) cells were used to evaluate the effect of TiO2 nanoparticles in aqueous solution.

The formation of the cells became slightly strange with the days increased. As observed by Alexa Fluor@488 Phalloidin staining, cells with TiO₂ nanoparticle were not directly damaging the F-actin, but we could see the TiO₂ nanoparticle which were adsorbed by the cells. The morphological changes of cells have been monitored by means of atomic force microsope (AFM). The measurement have been carried out in tapping mode in a liquid cell, to reproduce a cellular environment similar to the physiologic one. By atomic force microsope, the adhesion of the cells with TiO₂ nanoparticle were larger than the origin one. From the phase image, the cells bacame soft. The spread of the TiO₂ Reference

nanoparticle in the cells is discussed.

1. Jingkun Jiang, et al., J Nanopart Res (2009) 11:77–89

2. Masanori Horie, et al., Toxicology in Vitro 24 (2010) 1629–1638 3. Chan Jin, et al., Biol Trace Elem Res (2011) 141:3–15

Figure1. Atomic Force Microscope image of Mouse Fibroblast cells with TiO₂ nanoparticles

Surface-acoustic wave radio frequency identification system- design for the tag

中興大學 黃重浩

C.H.Huang (黃重浩), B.Y.Wang(王炳昱), Watson.Kuo(郭華丞), C.C.Wu(吳嘉哲) Department of Physics, National Chung Hsing University, Taichung, Taiwan Department of Mechanical Engineering

Abstract

, National Chung Hsing University, Taichung, Taiwan

Radio frequency identification (RFID) system is to use wireless communication to transfer data from a tag for identification and tracking. Unlike conventional IC tags, surface acoustic

wave(SAW) tags can be applied as fully passive tags in a RFID system. Here we report a work on SAW RFID tags focus on the 2.45GHz communication frequency. SAW tags were made on 128°Y-X cut lithium niobate (LiNbO₃) substrate, which is a well-known piezoelectric material. The

electromagnetic waves were received and transmitted via microstrip antenna, fabricated on

ceramics/glass composite circuit board. The incident electromagnetic waves, received by the antenna were transduced to Rayleigh waves on the substrate surface. As propagating on the surface, these Rayleigh waves may be reflected by reflectors. By tracing the time delay from the reflectors, one can identify the tag.

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Nanopore as a Platform for Devices ContainingNanoparticles and Stacked-Sheets

中央研究院 陳啟東 研究員

Linh-Nam Nguyen^1,2,3 (阮林南), Yann-Wen Lan¹ (藍彥文), Ming-Chou Lin¹ (林銘洲), Cen-Shawn Wu⁴ (吳憲昌), Watson Kuo⁵ (郭華丞), Minm-Tsong Lin⁶ (林敏聰),, and Lain-Jong Li⁷ (李連忠),

Chii-Dong Chen¹ (陳啟東)

1 Institute of Physics, Academia Sinica

2 Department of Engineering and System Science, National TsingHua University

3 Nano Science and Technology Program, Taiwan International Graduate Program, Academia Sinica

4 Department of Physics, National Chang-Hua University of Education

5 Department of Physics, National Chung Hsing University

6 Institute of Physics, National Taiwan University

7

Abstract

Institute of Atomic and Molecular Sciences, Academia Sinica

Nanopores made on Si₃N₄

In the first example, a ZnO-nanoparticle is placed onto the pore using an SEM-based nano-tip manipulator and then sandwiched from top and bottom with Al electrodes. The chemical potential of the nanoparticles is tuned by an electrode surrounding the nanoparticle. At 300K the device shows n-type behavior with a high electron mobility of 190cm

membranes are employed as a template platform for electronic devices containing individual single particles as well as layered-structured materials. In this talk, I will show the structure of the template and present its fabrication procedures, and the use of this template is illustrated with two examples.

2

In the second example, triple-stacked MOS

/Vs, a value much higher than that of ZnO films. Further, because of the strong capacitive coupling, the normalized transconductance is as high as 27.2μS/μm. On the other hand, the asymmetric device structure facilitates current-voltage rectification that enables photovoltaic capacity.

2 sheets layer were laid on top of the pore and covered with Al top and bottom electrodes. The inter-layer tunneling current is measured as a function of bias voltage as well as gate voltage. Because of asymmetrical structure, the device exhibits

diode-type behavior with a current peak arising from inter-layer resonant tunneling.

Reference

[1]. “Photo-response of a nanopore device with a single embedded ZnO nanoparticle”,

Nanotechnology, 23, 165201(2012). See also http://nanotechweb.org/cws/article/lab/49545

*e-mail: chiidong@phys.sinica.edu.tw, http://www.phys.sinica.edu.tw/~quela

(a) SEM image of a manipulation of single ZnO nanoparticle by using optical fiber probe. The scale bar is 500nm. (b) SEM image of the bottom side of the nanopore after placement of a ZnO nanoparticle. The scale bar is 100nm. (c)-(d) Schematic of single nanoparticle manipulation process: (c) shows disperse and capture of nanoparticles and (d) illustrates the placement and release processes. (e) Schematic illustration of the nanopore device containing a single ZnO nanoparticle sandwiched between top and bottom electrodes.

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Quantum confinement effect: its influence on the growth of metal films and applications

中央研究院 蘇維彬 研究員 Wei-Bin Su

Institute of Physics, Academia Sinica, Nankang, Taipei, Taiwan

Abstract

When the thickness of a metallic film is in the nanometer range, electrons in the film can manifest the quantum confinement effect to form quantum well (QW) states because of the wave nature.

Scanning tunneling microscopy (STM) combined with spectroscopy is a powerful tool to explore the QW states. Distinct QW states can be observed in the Pb films with STM. We demonstrate that the formation of the QW states in the Pb film can significantly affect the morphology, thickness, growth process and electronic structures of Pb films. On the other hand, Since the QW states are observed in real systems, its behavior will be affected by the properties of the system. In other words, QW states can be applied to explore the physical properties of metal films. By observing QW states, we demonstrate that there exists the screening effect in Pb films and the image potential effect outside Pb films. By analyzing the linewidth of QW states, the physical quantities about the electron-phonon and electron-electron interaction can be obtained. By observing energy shift of QW states, we find the existence of field-induced expansion deformation in Pb films. Moreover, when a bias voltage in STM is applied to make the Fermi level of the tip higher than the vacuum level of the sample, electrons can manifest another quantum confinement effect to form standing wave states in STM gap. We demonstrate that the standing wave states can be exploited to measure the work function of thin metal films with very high precision.

單光軸異向性引致表面磁光法拉第旋轉角的訊號震盪現象

嘉義大學 蘇炯武 教授 國立嘉義大學電子物理系

摘要

法拉第效應已經是一個發現將近有 170 年歷史的現象，然而隨著真空技術的進步、薄膜技 術之精進，讓此效應之原貌更加地清楚，也進一步發現當初觀察之限制瓶頸與不足，研究中除了 觀察到具備光學透明性之任何材料都具有一般法拉第效應外，在單光軸異向性晶體上成長磁性超 薄膜時，隨著成膜結構之過程中，發現特殊法拉第效應中法拉第旋轉角之廣角震盪行為，其中似 乎透漏出薄膜磁結構之完整性。本次發表著重在磁訊號與表面結構之議題討論，以作者所設計建 造之表面法拉第效應探測儀量測磁性訊號中發現，未經熱退火處理之室溫氧化鋅晶體材料表面仍 具有約一奈米深度的空間讓磁性薄膜形成完整磁區，尤其靈敏的法拉第旋轉角的入射角震盪現象 更隱約看出成長週期與結構相關，除了震盪行為來自於單光軸晶體之光學特性外，此現象之源由 應可進一步應用於光學元件之相位調整。

* E-mail:cwsu@mail.ncyu.edu.tw

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Current-induced magnetization switching of magnetic tunnel junctions

彰化師大 趙建都

C. T. Chao(趙建都)¹, C. Y. Kuo(郭政宜)¹, Lance Horng(洪連輝)¹, M. Tsunoda², M. Takahashi², and J.

C. Wu(吳仲卿)¹

1 Department of Physics, National Changhua University of Education, Taiwan

2

Abstract

Department of Electronic Engineering, Tohoku University, Japan

In the last decade or so, the switching characteristics of nano-scaled magnetic tunnel junctions have attracted tremendous interest due to their practical applications. Many efforts have been devoted to understand the current-induced magnetization switching because of its high scalibility. In this study, An MTJ stack film, consisting of bottom electrode/ CoFeB 4/ MgO 0.78/ CoFeB 3.6/CoFe 0.5/ Ru 0.85/

CoFe 2.5/ IrMn 7.5/ top electrode (thickness in nanometers), is patterned into a nano-scaled elliptical device by using standard electron beam lithography in conjunction with ion beam etching. The static magnetoresistance (MR) measurement was utilized to identify the MR ratio as well as the switching behavior driven by external magnetic field. Subsquently, a current pulse is employed to switch the magnetization configuration between low (parallel) and high (anti-parallel) states. In addition, the current-induced switching behaviors are characterized by a real-time single shot measurement. After the pulse rising, the profile shows a transition which implies the resistance variation. This incubation time between pulse onset and resistance change indicates the minimum operation time of a single device. The distribution of the incubation time represents strong correlation with current density and external magnetic field. More details will be elaborated.

Fig. 1 (a) The schematic of the measurement setup. (b) The typical MR curve with low sensing current of 1μA. (c) The pulse profile is observed by oscilloscope. Black curve shows that the magnetization is not switched. The red curve indicates that the resistance change from high to low state after a certain inbucation time.

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Extraordinary tunneling magnetoresistance by the mediation of iron nanoparticles embedded in the MgO based magnetic tunnel junction

彰化師大 李彥琦

Yen-Chi Lee¹, Chia-Hao Lin², Te-ho Wu² and Jong-Ching Wu^1*

1Taiwan SPIN research center, National Changhua Univ. of Education, Taiwan

2

Abstract

Taiwan SPIN research center, National Yunlin University of Science and Technology, Taiwan

Magnetic tunnel junctions (MTJs) that basically consist of two ferromagnetic (FM) layers sandwiching a thin oxide layer have been of great interest due to wide potential applications. In contrast to single barrier MTJs, double barrier MTJs (DBMTJs) are expected to show much higher magnetoresistance (MR) ratio, and indeed a rare study of more than 1000% MR ratio is reported [1].

Apart from high MR ratio of DBMTJs, many interesting phenomena have also been revealed such as spin-dependent Coulomb blockade [2], quantum well oscillation [3], and spin-dependent resonant tunneling [4]. In general, DBMTJs is constructed with two pinned layers separated by an insertion of free FM layer in the central insulating layer. The inserted layer may be in continuous or granular form, and this plays an important role for tunneling behaviors and/or switching properties. Herein, we report a study of a DBMTJ with the structure as follows:

CoFeB(1.86)/MgO(0.2)/Fe(0.1)/MgO(0.5)/CoFeB(0.6) (unit: nm). The stacked film is grown by a sputtering system followed by an annealing at 250 ℃ in the absence of any external fields. The annealed film and patterned film (4μm×6μm ellipse) are characterized using transmission electron microscopy (TEM), alternating gradient magnetometer (AGM), and MR measurements, respectively.

Figure 1(a) shows a TEM micrograph, in which the iron nanoparticles with lateral size 1.5 nm and thickness 1 nm are discernible. Figure 1(b) exhibits M-H curves with in-plane and out-of-plane magnetic field, respectively, with which one may conclude that the anisotropy of this stacked film is favorable in in-plane direction. Figure 2 demonstrates a typical in-plane MR curve and an anomalous out-of-plane MR behavior that shows a bell-shaped MR curve at low-field region followed by a linear MR variation beyond 0.2 kOe. This out-of-plane MR curve indicates a strong ferromagnetic coupling between two CoFeB layers. In addition, the iron nanoparticles play an important role of mediating the tunneling process. Therefor, the MR variation may be accounted with the relative magnetization orientations between iron nanoparticles and the coupled CoFeB layers [5], as illustrated in the insets to figure 2. More details will be discussed.

Reference

[1]. Lixian Jiang, Hiroshi Naganuma, Mikihiko Oogane, and Yasuo Ando, Appl. Phys. Expr. 2, 083002 (2009)

[2]. K. Yakushiji, S. Mitani, K. Takanashi, and H. Fujimori: J. Appl. Phys. 91, 7038 (2002) [3]. T. Nozaki, N. Tezuka, and K. Inomata, Phys. Rev. Lett. 96, 027208 (2006)

[4]. T. Niizeki, N. Tezuka, and K. Inomata, Phys. Rev. Lett. 100, 047207 (2008)

[5]. J. Carvell, E. Ayieta, A. Gavrin, Ruihua Cheng, V. R. Shah, and P. Sokol, Journ. Appl. Phys. 107, 103913 (2010)

15

Figure 2 H_c and H_in as a function of direct current of (a) sample 1 and (b) sample 2.

Figure 1 MR curves as a function of direct current taken from two sets of spin valve: (a) sample 1 and (b) sample 2. Note that the pinning direction and applied field direction are indicated in the insets.

Effect of direct current polarity on the magnetization reversal of high aspect ratio spin valve

彰化師大-郭政宜

C. Y. Kuo(郭政宜)¹, C. T. Chao(趙建都)¹, Lance Horng(洪連輝)¹, M. Tsunoda², M. Takahashi², and J.

C. Wu(吳仲卿)¹

1Department of Physics, National Changhua University of Education, Changhua, Taiwan

2

Abstract

Department of Electronic Engineering, Tohoku University, Sendai, Japan

We report a study on the magnetization reversal of a high aspect ratio spin valve, especially the effect comes from the direct current polarity. In order to possess a uniform magnetization, based on the shape anisotropy, in free layer elliptical spin valves, with long/short axis of 10/1 μm, are fabricated by using electron beam lithography in conjunction with ion beam milling. Non-magnetic electrodes are patched on both ends of the ellipse, thus a current-in-plane spin valve is ready for measurement. A low ac sensing current superimposed with various direct currents is used for the magnetoresistance (MR) measurements. Notice that the external magnetic field is applied parallel to the pinning direction, but the current is always flowing in long axis direction. In the presence of direct current an induced Oersted field should be considered as an important effect. In order to distinguish the contribution of the Oersted field, two kinds of devices with pinning direction aligned in short and long axis are fabricated and designated as sample 1 and 2, respectively. Figure 1 shows two sets of MR curves with pinning direction indicated in the inset for each set. Data in figure 1(a) reveal linear MR variation while the data MR in figure 1(b) manifest well-defined high/low MR states. In addition, the direct current polarity results in different switching properties in sample 1 and 2. Figure 2 shows the coercive field and MR curve shift (H_in) as a function of direct current. Obviously, the Oersted field induced by direct current is generated in short-axis direction. Therefore, for the case of sample 1, Oersted field is parallel to external magnetic field (pinning direction as well) and thus enhances/suppresses effective magnetic field by applying negative/positive direct current. Hence, the Hin increased with increasing direct current, but no influence on the coercive field (H_c), as shown in Fig. 2(a). For the case of sample 2, the induced Oersted field is orthogonal to the external field and thus assists to the reversal of free layer.

Consequently, the transverse Oersted field reduces H_c and shows no influence on Hin. Furthermore, figure 2(b) shows an asymmetry H_c (I) behavior, the maximum of H_c(I) occurs at 1.6 mA, and H_in(I) reveals a drop at 1.6 mA. Therefore, in addition to induced Oersted field it is believed that spin transfer torque effect should be taken into account.

16

Confocal microscope with long optical path under lower temperature

中興大學-余彥模

Cheng-Steam Li (李承烝),¹ and Ling-Wei Hung (洪苓瑋)²

1 Department of Physics,National Chung Hsing University

2

Abstract

Department of Physics,National Chung Hsing University

In this paper, we design a confocal scanning detector for the optical measurement of

telecommunications signals with long optical path up to 1600mm.This system can detect the electrical and CCD real-time monitoring of a sample, or using a laser light source to excite the sample

fluorescence for observing the images of confocal plane. This system is more 10 times of aberration than general microscope result the system length up to 1600mm

.

Therefore, lens design of imaging is the key to system success or failure. At the first generation of confocal microscopy developed by our laboratory, it can take the image of the CCD monitoring with 4.5x magnification and the resolution about 3.42μm. In this paper, we will try the different lens combinations for improvement magnification and resolution. In a series of the lens simulation and composed by using the optical simulation software ZEMAX, we successfully design a confocal microscopy with10x magnification, 2.4μm resolution, and the laser spot is about 2μm.

Half-reflecting mirror

Dichroic mirror Detector

Pinhole

Laser

17

Dipolar Coupling Array of Perpendicular to Plane Polarizer Spin-Torque Nano-Oscillators with Any Number

彰化師大 陳浩軒

HaoHsuan Chen¹, JuiHang Chang², ChingMing Lee³, JongChing Wu¹, Lance Horng¹, and ChingRay Chang²

1Department of Physics, National Changhua University of Education, Changhua, Taiwan, R.O.C.

2Department of Physics, Center for Nanostorage Research, and National Center for Theoretical Sciences, Nation Taiwan University, Taipei 10617

Abstract

, Taiwan, R.O.C.

Due to high frequency emissions, a high level of integration, and a high quality factor, spin-torque nano-oscillator(STNO) has been a new field of spintronics for both fundamental analysis and potential applications since 2003. In general, STNO is composed of F/n/P or F/I/P trilayers. Where P is the thicker magnetic layer with a pinned magnetization, F is the thinner one with a free magnetization, and n or I are non-magnetic metal and insulator layer respectively. When the pinned layer P provides a large enough dc spin-polarized electron current to the free layer F to cancel the damping effect of the magnetization, a stable precession of magnetization can be excited at several GHz frequencies.

Through Giant Magnetoresistance (GMR) or Tunneling Magnetoresistance (TMR) among the pinned and free layers of nanopillar, the precessional magnetization can be converted into microwave signals.

Thus, STNOs have huge potential for applications in GHz-range telecommunications that feature a tunable external magnetic field and use a dc current. Nevertheless, the output microwave power of a single STNO is only around several pico- or nano-watts, still too low for any practical applications.

Recently, lots of studies provide all kinds of schemes to raise the output power of STNOs through some coupling mechanisms such as electrical coupling, dipolar coupling, and spin wave

excitation.

In our work, we provide a scheme that makes multiple perpendicular to plane polarizer (PERP) STNOs that is based on nano-pillar to be stacked vertically very closely and connected in series,

References

like in Fig.1. Therefore, there exists dipolar interactions between free layer moments of these STNOs. From theoretical analysis of Macrospin model, i.e. LLG equation, under a strong demagnetization field in each STNO in the array, we find that the dipolar coupling required an antiferromagnetic-like phase locking state and thus the amplified amplititude microwave can be extracted through analyzers with antiferromagnetic-like state even if the sub-neighbor couplings are taken into account, as shown in Fig.

1. Moreover, in the simulation of five asymmetric STNOs with different natural frequencies, if the dipolar coupling is turned on, the time domain of microwave signals will become coherent compared with no dipolar coupling case like in Fig. 2.(a). Consequently, in the output power spectrums the five separate peaks will be merged into a single one by the dipolar coupling and their peak values will be magnified 25 times, as shown in Fig. 2(b).From the theoretical and numerical analysis, we can expect that dipolar coupling array that is based on PERP STNOs with nanopillar structure will become one of the good candidates for microwave power emission device.

1. H. H. Chen, J.H. Chang, and C. R. Chang, SPIN,1,1(2011) (接下頁圖)

18

Fig 1.

Structure of N serially connected STNOs in parallel with a load Rl. I_dc is the dc current source.The thicker layers P1 to PN denote the pinned layers and their moments all are perpendicular to the free layer's easy plane. The thinner layers F1 to FN

are the free layers. The layers A_i are analyzers that can switch the precessions of F_i into microwave signals through GMR effect.

Fig 1.

(a)Time domain of the microwave signal. A is dipolar coupling strength. αis the Gilbert damping constant. u’is the spin-transfer torque strength. (b) Power spectrum of the microwave signal.

19

Study of the interaction between vortices and different composite arrays in superconducting Nb film

彰化師大-楊婕妤

Shirley Yang (楊婕妤)¹, Sheng Hao Wang (王聖豪)¹, Tian-Chiuan Wu (吳添全)² (吳仲卿)

, Jong-Ching Wu

3, Lance Horng (洪連輝)³

1Department of Physics, National Changhua University of Education, Changhua, Taiwan;

2Department of Electronic Engineering, National Formosa University, Yunlin, Taiwan;

3

Abstract

Department of Physics and Taiwan SPIN Research Center, National Changhua University of Education, Changhua, Taiwan

The mixed state is a special phenomenon that the magnetic field will enter into superconductor while the resisitivity still remains zero in type-II superconductors. Efficient defects would pin vortices so pinning arrays are made to enhance the critical current. Series of pinning arrays are added at the center of every hexagonal cell. The defect diameter of every hexagonal cell is 300 nm and the spacing between the pinning sites is 400nm. The diameters of the defect at the center of the hexagonal are 0, 100, 200, and 300 nm. Irregular spacings of matching fields were found in the composite arrays. Also, interstitial vortex was observed at the center of the honeycomb arrays in the simulation.

References

[1]. J, I. Martin, M. Velez, J. Nogues, and I. K. Schuller, Phys. Rev. Lett. 79,1929 (1997) [2]. Y. Otani, B. Pannetier, J. P. Nozieres, D. Givord, J. Magn. Magn. Mater. 126, 622 (1993) [3]. Lance Horng, T. C. Wu, J. C. Wu, R. Cao, and T. J. Yang, J. Appl. Phys. 101, 09G113 (2007)

FeSeTe superconductive thin film by sputter system

中興大學 許詩怡 Shih-I Hsu, Chiu-Hsien Wu

Department of Physics, National Chung Hsing University Abstract

There are many discovery of iron-based in recent, which makes a huge enthusiasm for extensive research on these materials. Since this kind of high-temperature superconductor family is discovered, it becomes second high-temperature superconductor after the copper oxide superconductor and scientists begin looking forward a better qualities of these new materials.

FeSeTe has already been investigated and published widely. Trying to start from making bulks, we exam the structure and component by XRD and EDX. The sample resistance was measured by using the standard four-probe method using silver paste for contact in low-temperature measurement system to detect the superconductivity. Furthermore, we expect that the material FeSeTe could show

superconductivity by Sputter system considered that most of FeSeTe thin film all made up by PLD.

However, there are still plenty of works on the film like Josephson junctions, etc, in the followings.

Aim to be successful in these procedures.

References

1. F.C. Hsu, J.Y. Luo, K.W. Yeh, T.K. Chen, T.W. Huang, P.M. Wu, Y.C. Lee, Y.L. Huang, Y.Y. Chu, D.C. Yan, M.K. Wu, Proc. Natl. Acad. Sci. USA 105 (2008) 14262.

2. Growth of superconducting FeSe0.5Te0.5 thin films by pulsed-laser deposition Y. Imai a,c,*, T.

Akiike a,c, R. Tanaka a,c, H. Takahashi a,c, M. Hanawa b,c, I. Tsukada b,c, A. Maeda a,c 3. Enhanced superconducting transition temperature in FeSe0.5Te0.5 thin films Weidong Si,a_

Zhi-Wei Lin, Qing Jie, Wei-Guo Yin, Juan Zhou, Genda Gu, P. D. Johnson, and Qiang Lib_Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA_Received 17 June 2009; accepted 14 July 2009;

published online 3 August 2009

Low-temperature fabrication of superconducting FeSe thin films by pulsed laser deposition Ta-Kun Chen a,, Jiu-Yong Luo a, Chung-Ting Ke a, Hsian-Hong Chang b, Tzu-Wen Huang a, Kuo-Wei Yeh a, Chung-Chieh Chang a, Po-Chun Hsu a, Chun-Te Wu b, ing-Jye Wang c, Mau-Kuen Wu a

20

Properties of FeSeTe Microbridge fabricated by Focus Ion Beam

中興大學 張為淳

Wei-Chun Chang (張為淳),¹ and Chiu-Hsien Wu(吳秋賢)¹²

1 Department of Physics, National Chung-Hsing University, Taichung City, 402,Taiwan

2

Abstract

Institute of NanoScience, National Chung-Hsing University, Taichung City, 402,Taiwan

Josephson junctions with iron based superconductor have been intensively investigated in recent years.

We have fabricated the FeSeTe bridges 384-674nm in width on MgO substrates by a focused ion beam (FIB), studied current-voltage I-V characteristics, The temperature-dependent critical current, and the normal-state resistance. At 4.2 K, the current-voltage curves showed the characteristics of an S-N-S Josephson junction.

The magnetic field dependence of the critical current shows a variation of I_c in the positive as well as in the negative bias branch, but does not suppress it completely. Also the influence of microwave irradiation on the junctions is shown. Thereby I_c

References

can be suppressed, while first order Shapiro steps can be observed.

[1]. S D¨oring1, et al. , Supercond. Sci. Technol. 25 (2012) 084020

[2]. E. Stepantsov, M. Tarasov, M. Naito, A. Tsukada, and D. Winkler, Appl, Phys. Lett. 89, 213111 (2006);

[3]. Soon-Gul Lee, Sung-Hak Hong, Won Kyung Seong, and Won Nam Kang, Appl. Phys. Lett. 95, 202504 (2009)

The Microstructure and Electrical Properties of YBCO Microbridge with Variable Thickness Fabricated by Focused Ion Beam

中興大學 吳函樺

H.H.Wu(吳函樺), Y.Z. Su(蘇于宗), C.H.Wu(吳秋賢)

Department of Physics, National Chung Hsing University, Taichung 402, Taiwan

Abstract

In this paper, controlled the thickness about the link region produced by the microbridges of high-temperature superconducting YBCO (YB₂C₃O_7-δ

YBCO microbridges were fabricated with widths of 5- 8μm and thickness 150 nm using standard techniques of photolithography and Ar

).In this thesis, Focus Ion Beam (FIB) was used to control different thickness of YBCO microbridges. And when the thickness of the microbridge was controlled under the nanometer scale, it showed weak link behavior.

+ ion milling. To control the thickness of the micro-bridge was maintained between 40 and 90 nm. Using field-emission transmission electron microscope (FE–TEM) to observe the structure of the Variable Thickness Bridge (VTB), Ga⁺ damages horizontally and vertically into the amorphous structure about 20-30 nm. When the thickness was below 40 nm, there was little complete part of YBCO structure in the bottom. As the thickness of the micro-bridge decreased, critical temperature (T_c) and critical current (I_c

References

) became smaller. The successful recovery of oxygen content during the annealing process, the superconductivity of the microbridge became better.

[1]. B.D.Josephson, Physics Letters,1,251-253(1962)

[2]. W.F.Avrin and M.B.Simmonds,IEEE.Tran.Mag.27,3359(1991)