I.Surface Magnetism (Magnetic Ultrathin Film): 

1. d-band filling effect on magnetic anisotropy in low-dimensional magnetic system (ultrathin film): By varying alloy composition of FexNi1-x and CoxNi1-x ultrathin films on Cu(100) as well as Cu3Au(100) (partly in cooperation with Dr. K. J. Song, IAMS, Academia Sinica) with invariant structure, we investigated the critical evolution of spin-reorientation transition behavior, and extracted the d-band filling (or d-electron number) effect and strain relaxation effect on the magnetic anisotropy. These results can be well explained by a magnetoelastic model with composition-dependent anisotropy coefficients. (Phys. Rev. B 62, 14628 (2000) and Phys. Rev. B 71, 184413 (2005))

2. Critical evolution of metastable γ-Fe growth at variation of lattice parameter of buffer layer: Complicated interplay between magnetism and structure of γ-Fe (fcc Fe) is one of the most important issues in research of magnetic ultrathin film. Upon FexMn1-x alloy buffer layer with varying lattice parameter by changing its composition, “thick”γ-Fe(“pure”fcc Fe) films up to 30 ML was successfully stabilized (Phys. Rev. B 74, 224430 (2006)). This γ-Fe film revealed nonferromagnetic behavior, being consistent with the theoretical results from the first principle calculation.

3. Crystalline structure and antiferromagnetism of γ-Mn films on Cu3Au(100) (partly in cooperation with Dr. K. J. Song, IAMS, Academia Sinica): γ(fcc)-Mn, which exists at ~ 1400 K in bulk material, can be successfully prepared on Cu3Au(100) at room temperature due to the small lattice mismatch. The γ-Mn films precede a thickness-dependent structural transition from fcc to fct. Significant exchange bias is also observed in Fe/RT-Mn bilayers. (J. Appl. Phys. 97, 10K112 (2005) and Phys. Rev. B 75, 054419 (2007))

4. Spin-reorientation transition in ferromagnetic/antiferromagnetic exchange coupled systems (ongoing and partly in cooperation with Dr. Wei in NSRRC): In Fe/fcc-Mn/Cu₃Au(001) bilayer, we found that the easy axis of Fe layer can be changed from in-plane to perpendicular direction with the increasing thickness of adjacent AFM fcc-Mn layer. The corresponding coercivity enhanced with increasing Mn thickness demonstrates that the switching of easy axis is due to the exchange coupling between Fe and Mn layers.

5. Magnetic imaging by spin-polarized scanning tunneling microscopy: We have set up a new kind of ring-shape tip with Fe-coated W wire as the spin sensitive tip for SP-STM. The ring-shape tip with stable in-plane magnetization can allow probing the magnetic systems with in-plane magnetization (Appl. Phys. Lett, 91, 202507 (2007)).

6. In situ magnetization switching of magnetic probes applied to spin-polarized scanning tunneling microscopy: Soft magnetic tip was utilized to be the probe of spin-polarized scanning tunneling microscopy. It was demonstrated that the spin contrast can be reversed by in situ switching tip magnetization through varying tip-substrate distance for resolving perpendicular magnetic domain images. With this in situ magnetization direction switching of the soft magnetic tip, it is conceivable to separate magnetic from chemical and topographic contributions without applying external magnetic field. This provides an effective tool for the study of complex magnetic spin structures with various nonmagnetic impurities or compositions involved (Appl. Phys. Lett, 96, 142515 (2010)).

Fig. 1. (a) Spin polarized conductance mapping image of 0.66 ML bilayer high Co nanoislands and the black spots on the surface of Co nanoislands are segregated Cu atoms. The corresponding topography is shown in the inset. (b) Reversed spin contrast image taken after the magnetization switching of front tip end. (c) Similar spin contrast image to the (a) taken after tip magnetization reverse again. (image sizes are all 85 x 85 nm², taken at U=−0.3 V and I=+1.0 nA). 

Ⅱ.（Organic）Spintronics: 

1. High Frequency Magneto-Impedance for MTJ (ongoing; partly in cooperation with ITRI): High frequency response and magneto-impedance behavior in MTJ or magnetic nanostructure attract much interest due to the high frequency application of spintronics devices, such as MRAM and high speed communication component. A detailed study of high frequency impedance will be performed in an offset dc environment. The frequency and dc offset dependence will be also simulated by a magnetoelectrical model. (J. Appl. Phys. 107, 093904 (2010)) 

2. Spin transport of organic/inorganic hetero-structure (ongoing): Since the organic and molecule are famous for the long spin-diffusion length, the application in spintronics holds great promise in recent years. We fabricate and investigate transport properties of organic spin valve. At room temperature, we observed the magnetoresistance versus magnetic field in our organic spin-valve. The two steps hysteresis loop evidences the parallel and anti-parallel state of organic spin valve.

Ⅲ.Zero-Dim. and One-Dim. Functional Nanomaterials： 

1. Supported magnetic nanoclusters on Si-N (partly in cooperation with Prof. Gwo in NTHU): Metallic Co, Fe, Ni nanoclusters (1.5 nm diameter) with narrow size-distribution were grown, by using MBE, on a single crystal Si3N4(0001) film. This finding is proposed to be due to quantum effect of the 4s electronic shell in the 3d-transition element, providing a new kind of fabrication method for nanodots (electronic growth). (Phys. Rev. Lett. 90, 185506 (2003)).

2. One-dimensional chain alignment of metallic nanoclusters on oxide layers (ongoing; partly in cooperation with Dr. K. J. Song, IAMS, Academia Sinica): Co nanodots were prepared on selective single crystal oxide layer with high thermal stability and one-dimensional chain alignment along the fine structure of the oxide layer surface. A slow deposition rate at low temperature promises the good linear alignment. Besides, capping of Cu overlayer on Fe and Co nanoparticle assembly induces significant Tc enhancement. This may provide an excellent system for application in catalyst and in magnetic nanostorage. (Appl. Phys. Lett. 86, 34105 (2005), Appl. Phys. Lett. 88, 153117 (2006), and Appl. Phys. Lett. 89, 153111 (2006)). 

3. Electronically patterning through one-dimensional nanostripes with high density of states on single-crystalline Al₂O₃ domain. Self-assembled one-dimensional nanostripes on the single-crystalline Al₂O₃ domains are found to be the nucleation sites of nanoparticles through an enhanced density of states observed by the scanning tunneling microscopy and spectroscopy. Bias-dependent topographic images and the conductivity spectra indicate that these nanostripes have both enhanced occupied and unoccupied states within the oxide bandgap. These more metallic nanostripes have stronger electronically trapping ability than the oxide domain, which can be used as a one-dimensional electronically self-patterned template for the guided growth of nanostructures (Appl. Phys. Lett. 93, 143104 (2008)).

4. Enhanced chemical shift of carbon nanotube from laser assisted gas incorporation (partly in cooperation with Dr. Chen in NSRRC): We investigate the position-selected electronic structure of laser modified CNTs by scanning photoemission electron microscopy (SPEM) of CNTs in air and N2 environment, the modified region shows enhanced chemical shifts in carbon 1s state, respectively. The modification of electronic structure is shown to be strongly dependent on the gaseous environment. We demonstrate an effective post growth process to modify the electronic structure of CNTs for further applications (Appl. Phys. Lett. 91, 183101 (2007)).

5. Tuning of magnetism in ferromagnetic thin films by reversing the functional groups of molecular underlayer: We demonstrate a molecular approach of tuning the magnetic properties of ferromagnetic thin films by reversing the functional groups of the organic underlayer. For the CoFe/Langmuir–Blodgett (LB) film system, we find that the coercivity of CoFe thin films from 4 to 10 nm_ made on hydrophobic surfaces is significantly enhanced whereas that on hydrophilic surfaces remains unchanged, as compared with the films directly on glass substrates. These findings suggest an alternative way for tuning the magnetic properties of the FM layer by LB film in which the functional groups play an important role (Appl. Phys. Lett. 96, 262502 (2010)). 

6. Interface control in organic/inorganic hetero-structure (ongoing and partly in cooperation with Dr. Pai in Center for Condensed Matter Sciences, NTU). Since the organic and molecule are famous for the long spin-diffusion length, the application in spintronics holds great promise in recent years. However, it still has some challenges in the control of interface. We first study the growth and surface structure of molecule (1 ML C₆₀) on Cu(001) by STM. By tuning annealing temperature of 648 K, there are two kinds of structures at this meta-stable state, which are two bright and one dim row, and one bright and one dim row. However, when the annealing temperature is arising to 736 K, all one bright and one dim rows disappear, and only two bright and one dim rows along two directions is presented to be stable state. (Phys. Rev. B82, 12544 (2010))

FIG 2. STM images of 3-13 ML Fe nanoparticle assembly on Al₂O₃//NiAl(100). The particle size increases with coverage, and the shape of particles sustains up to 13 ML.

FIG 3. (a) The schematic diagram of oblique focused laser beam to prune CNTs in the selected gaseous environment. (b) and (c) Cross-sectional SEM image and corresponding SPEM image.

1. Ultra High Vacuum (UHV) System
2. Molecular Beam Epitaxy (MBE)
3. UHV-Magneto-Optical Kerr Effect (MOKE)
4. Auger Electron Spectroscopy (AES)
5. Medium Energy Electron Diffraction (MEED)
6. Low Energy Electron Diffraction (LEED & I/V-LEED)
7. UHV-VT- Scanning Tunneling Microscopy (VT-STM)
8. UHV- LT- Scanning Tunneling Microscopy (LT-STM)
9. UHV-Spin-polarized Scanning Tunneling Microscopy (SP-STM)
10. Photoemission electron Microscopy (PEEM) 
11. Scanning Photoelectron Microscopy (SPEM)