Le, Hong Quang; Chua, Soo-Jin; Fitzgerald, Eugene A.; Loh, Kian Ping
The ZnO nanorods with the length of 1-1.5 μm
were deposited on p-GaN by hydrothermal synthesis at low temperature 100°C. The structural and optical properties of the as-grown ZnO rods were investigated by X-Ray
diffraction (XRD) and photoluminescence (PL) spectra. After annealing treatment the as-grown films in air at 600°C,
30min, and the ZnO rods showed good crystallinity and optical properties with strong UV emission at 378 nm. In addition, a sharp UV emission peak at 369.45 nm with the
FWHM 20 meV, which attributed to the bound exciton recombination, was also observed from the ZnO rods at 80K. Next, the e-beam evaporation method...
Yu, Hongpeng; Pey, Kin Leong; Choi, Wee Kiong; Chi, D.Z.; Fitzgerald, Eugene A.; Antoniadis, Dimitri A.
Continual scaling of the CMOS technology requires thinner gate dielectric to maintain high performance. However, when moving into the sub-45 nm CMOS generation, the traditional poly-Si gate approach cannot effectively reduce the gate thickness further due to the poly-depletion effect. Fully silicided Ni metal gate (FUSI) has been proven to be a promising solution. Ni FUSI metal gate can significantly reduce gate-line sheet resistance, eliminate boron penetration to channels and has good process compatibility with high-k gate dielectric. But Ni FUSI has a mid-gap workfunction which is not suitable for high-performance CMOS applications where the band-edge workfunction is required. In...
Chew, Han Guan; Choi, Wee Kiong; Chim, Wai Kin; Foo, Y.L.; Fitzgerald, Eugene A.
Germanium (Ge) nanocrystals had been synthesized by annealing co-sputtered SiO₂-Ge in N₂ and/or forming gas (90% N₂ + 10% H₂) at temperatures ranging from 700 to 1000°C from 15 to 60 min. It was concluded that the annealing ambient, temperature and time have a significant influence on the formation and evolution of the nanocrystals. We also showed that a careful selective etching of the annealed samples in hydrofluoric solution enabled the embedded Ge nanocrystals to be liberated from the Si oxide matrix. From the Raman results of the as-grown and the liberated nanocrystals, we established that the nanocrystals generally experienced...
Koh, Yaw Koon; Chiang, Yet-Ming; Wong, Chee Cheong
Colloidal crystals are 3D nanostructures formed by self assembly of nanoparticles in suspension. The interaction forces between the colloid particles are expected to affect the ordering and the defect density in the resultant crystal. Based on this insight, the effect of ionic strength on the quality of the colloidal crystal is examined. It is found that at intermediate ionic strength, it is possible to get the best ordering of the colloidal crystal. The reason for this is explained based on previous work on the structural changes in an assembling colloidal crystal. A method for reducing the defect density in colloidal...
Fu, X.L.; Li, Yi; Schuh, C.A.
The homogeneous deformation of Zr-based bulk
metallic glass composites is studied near the glass transition temperature, at various levels of reinforcement volume fraction. Through examination of the constitutive response, it is seen that the presence of in-situ reinforcements increases the flow resistance of the glass dramatically. This strengthening effect is shown to arise from two separate contributions: load transfer from the amorphous matrix to the reinforcements,
and changes to the glass composition and structure upon in-situ precipitation of reinforcements.
Zheng, J.X.; Ceder, Gerbrand; Chim, Wai Kin; Choi, Wee Kiong
In this study, the native point defects including oxygen vacancy and interstitial, metal (La, Al) vacancy and interstitial, and metal antisite in perovskite LAO are studied. Defect formation energies are studied as a function of the external chemical potentials and Fermi level. The stable defects are identified under different external chemical potentials and Fermi levels. The effect of image charge corrections is also investigated. Finally, based on results in this study, optimal growth conditions can be proposed to achieve better defect engineering for LAO gate dielectrics.
Hartono, Haryono; Soh, C.B.; Chua, Soo-Jin; Fitzgerald, Eugene A.
A simple and cost-effective Si-doped porous GaN is fabricated by UV-enhanced electrochemical etching. An optimum current density of 20 mA/cm² applied for an hour in dilute NaOH solution produces a high density of uniform pores. Cross-section TEM reveals that etching takes place along the (0001) direction. A red shift of 0.7 cm⁻¹ in the E₂(high) phonon peak of GaN from micro-Raman indicates a relaxation of compressive stress in the porous GaN surface with respect to the underlying single crystalline epitaxial GaN. Subsequent growth of GaN layer on the porous template results in air gap formation, which is believed to serve...
Xia, H.; Meng, Shirley Y.; Lu, Li; Ceder, Gerbrand
Preferred c-axis oriented LiCoO₂ thin films were prepared on the SiO₂/Si (SOS) substrates by pulsed laser deposition (PLD). Thin film electrodes without carbon and binder are ideal samples to study the electrochemical properties of materials. We did galvanostatic charge/discharge measurements between 3 and 4.7 V on the Li/LiCoO₂ cell to study its electrochemical behavior. Potentiostatic intermittent titration technique (PITT) was used to measure the Li diffusivity in the LixCoO₂ film at different Li concentrations (0.15 < x < 0.75). The dependence of Li diffusivity on the c-lattice parameter and valence of cobalt ions is discussed.
Fu, X.L.; Li, Yi; Schuh, C.A.
Macroscopic ductility is promoted in bulk metallic glasses by both composite reinforcements (at low temperatures) and by the activation of viscous flow mechanisms (at high temperatures). It is of fundamental interest to understand deformation physics when both of these strategies are employed at the same time. Despite the quickly growing literature around the room-temperature mechanical properties of metallic glass matrix composites (MGMCs), the deformation behavior of MGMCs over a wide range of temperatures and strain rates has yet to be systematically investigated, especially at high temperatures close to Tg. Here the high temperature compressive behavior of Zr-based MGMCs with in-situ...
Yu, H.P.; Pey, Kin Leong; Choi, Wee Kiong; Chi, D.Z.; Fitzgerald, Eugene A.; Antoniadis, Dimitri A.
Continual evolution of the CMOS technology requires thinner gate dielectric to maintain high performance. However, when moving into the sub-65 nm CMOS generation, the traditional poly-Si gate approach cannot effectively reduce the gate thickness further due to the poly-depletion effect. Fully silicided metal gate (FUSI) has been proven to be a promising solution. FUSI metal gate can significantly reduce gate-line sheet resistance, eliminate boron penetration to channels and has good process compatibility with high-k gate dielectric. In this paper, the effect of oxygen introduced by the process of conventional furnace annealing in FUSI metal gate is investigated.
A 120 nm...
Chew, Han Guan; Choi, Wee Kiong; Foo, Y.L.; Chim, Wai Kin; Fitzgerald, Eugene A.; Zheng, F.; Samanta, S.K.; Voon, Z.J.; Seow, K.C.
Growth and evolution of germanium (Ge) nanocrystals embedded into a silicon oxide (SiO₂) system have been studied based on the Ge content of co-sputtered Ge-SiO₂ films using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy. It was found that when the proportion of Ge relative to Ge oxide is 20%, TEM showed that annealing the samples at 800°C for 60 min resulted in the formation of a denuded region between the silicon/silicon oxide (Si/SiO₂) interface and a band of Ge nanocrystals towards the surface of the film. By introducing a 20nm thick thermal oxide barrier on top of the silicon...
Zheng, J.X.; Ceder, Gerbrand; Maxisch, T.; Chim, Wai Kin; Choi, Wee Kiong
Yttria (Y₂O₃) has become a
promising gate oxide material to replace silicon dioxide in metal-oxide-semiconductor (MOS) devices. The characterization of native point defect in Y₂O₃ is essential to understand the behavior of the material. We used the first-principles pseudopotential method to study the electronic structure, defect structure and formation energy of native point defects in Y₂O₃. Vacancies, interstitials and antisites in their relevant charge states are considered. The dominant defect types are identified under different chemical potentials and different Fermi levels. Oxygen vacancies are the dominant defect types under high yttrium chemical potential condition. Lower yttrium chemical potential leads to oxygen...
Koh, Yaw Koon; Wong, Chee Cheong
Defect control in colloidal crystals is essential for these nanostructures to be effective as photonic bandgap (PBG) materials. We have used in-situ monitoring of the PBG of a colloidal crystal to study the structural changes during colloidal self assembly, with a focus on the formation of macroscopic defects such as cracks. These findings allow us to model the final stages of colloidal self assembly and explain the formation of growth defects in colloidal crystal. Our model suggests that cracks are intrinsic to self assembly growth methods. . However, by tuning the interaction potential between the colloids, it is possible to...
Chen, A.; Chua, Soo-Jin; Wang, B.; Fitzgerald, Eugene A.
The fabrication process of two-dimensional photonic crystals in an AlGaInP/GaInP multi-quantum-well membrane structure is developed. The process includes high resolution electron-beam lithography, pattern transfer into SiO₂ etch mask by reactive ion etching, pattern transfer through AlGaInP/GaInP layer by inductively coupled plasma (ICP) etching and a selective undercut wet etch to create the freestanding membrane. The chlorine-based ICP etching conditions are optimized to achieve a vertical sidewall. The photonic crystal structures with periods of a=160-480nm are produced.
Quang, Le Hong; Chua, Soo-Jin; Fitzgerald, Eugene A.
We report on the characteristics of a ZnO based metal insulator semiconductor (MIS) diode comprised of a heterostructure of n-ZnO nanorods/n-GaN. The MIS structure consisted of unintentional - doped n type ZnO nanorods grown on n-GaN sample using hydrothermal synthesis at low temperature (100°). The ZnO nanorod layer was vertically grown from the GaN sample, having the diameter 100nm and length 2µm. Then, an insulator layer for electrical isolation was deposited on the top of ZnO nanorod layer by using spin coating method. A metal layer (gold) was finally deposited on the top. The I-V dependences show a rectifying diode...
Hartono, Haryono; Chen, P.; Fitzgerald, Eugene A.; Chua, Soo-Jin
InN has been grown on GaN with a thin intermediate layer of InGaN by metalorganic chemical vapor deposition (MOCVD) to further enhance indium incorporation in subsequent InGaN layer. Trimethylindium (TMI) and ammonia (NH₃) were used as the source for InN growth and transmission electron microscopy (TEM) confirmed the presence of pyramid-like structure of InN. A layer of InGaN subsequently grown on top of these InN pyramids shows a red-shift of ~20 nm relative to InGaN layer grown directly on GaN using the same growth condition. However, there is no significant pits reduction. An alternative method to enhance indium incorporation is...
Leong, Hoi Liong; Gan, C.L.; Pey, Kin Leong; Thompson, Carl V.; Li, Hongyu
Bonded copper interconnects were created using thermo-compression bonding and the dicing yield was used as an indication of the bond quality. SEM images indicated that the Cu was plastically deformed. Our experimental and modeling results indicate that the effective contact area is directly proportional to the applied load. Furthermore, for first time, results have been obtained that indicate that the dicing yield is proportional to the measured bond strength, and the bond strength is proportional to the effective contact area. It is also shown that films with rougher surfaces (and corresponding lower effective bonding areas) have lower bond strengths and...
Xia, Hui; Lu, Li; Ceder, Gerbrand
LiNi₀.₅Mn₁.₅O₄ thin films have been grown by pulsed laser deposition (PLD) on stainless steel (SS) substrates. The crystallinity and structure of thin films were investigated by X-ray diffraction (XRD). Microstructure and surface morphology of the thin films were examined using a field-emission scanning electron microscope (FESEM). The electrochemical properties of the thin films were studied with cyclic voltammetry (CV) and galvanostatic charge-discharge in the potential range between 3.0 and 4.9 V. The electrochemical behavior of LiNi₀.₅Mn₁.₅O₄ thin films showed reversible capacity above 4.7 V and good cycle performance up to 50 cycles.
Wang, C.Y.; Ceder, Gerbrand; Li, Yi
Al based alloy powders (Al₈₅Ni₅Y₆Co₂Fe₂) are produced by spray atomization method. High energy ball milling is done to modify the surface topology and particle size for better electrochemical performance. X ray diffraction (XRD), differential scanning calorimeter (DSC), scanning electron microscope (SEM) and transmission electron microscope (TEM) were conducted to characterize the microstructure of the alloys after ball milling. It is found that 5 hours ball milling gives the minimum crystallization and structure change. Thin film sample is also deposited on stainless steel substrate by pulsed laser deposition (PLD) method for electrochemical test. The capacity and reversibility for different samples are...
Chang, Choon Wai; Choi, Z.-S.; Thompson, Carl V.; Gan, C.L.; Pey, Kin Leong; Choi, Wee Kiong; Hwang, N.
Three terminal âdotted-I’ interconnect structures, with vias at both ends and an additional via in the middle, were tested under various test conditions. Mortalities (failures) were found in right segments with jL value as low as 1250 A/cm, and the mortality of a dotted-I segment is dependent on the direction and magnitude of the current in the adjacent segment. Some mortalities were also found in the right segments under a test condition where no failure was expected. Cu extrusion along the delaminated Cu/Si₃N₄ interface near the central via region was believed to cause the unexpected failures. From the time-to-failure (TTF),...