[show abstract][hide abstract] ABSTRACT: Electron phonon (el-ph) coupling is a fundamental quantity that controls the electron transport through a conductor. We experimentally determined the el-ph coupling strength of epitaxial copper (Cu) films ranging from 5 to 1000 nm thick using both ultra-fast, optical pump-probe reflectivity and temperature-dependent resistivity measurements. An enhancement of the el-ph coupling strength was observed when the thickness of the films was reduced to below 50 nm. We suggest that this unexpected enhancement of the el-ph coupling strength is partially responsible for the observed increase of resistivity in the films below 50 nm thick.
[show abstract][hide abstract] ABSTRACT: As line width decreases below 15 nm, the diffusion barriers used in
copper (Cu) technology in high performance integrated circuits
significantly increase the overall resistivity of interconnects. In this
work, we argue that the performance of pure W and Mo lines with line
widths smaller than 15 nm could be better than that of Cu lines with
barriers. We, herein, present a process of creating Cu, W and Mo metal
nanolines on Si substrates using the combination of e-beam lithography
(SUPRA 55 Scanning electron microscopy), oblique angle deposition, and
lift-off techniques. The integrity of the sub-15 nm nanolines, including
the line edge roughness, will be quantified. We shall also report our
attempts to measure the resistivity of these nanolines using four point
probe techniques. The relative contributions of phonon scattering versus
surface scattering will be discussed. The effect of line edge roughness
to the overall resistivity will also be presented.
[show abstract][hide abstract] ABSTRACT: Terahertz differential time-domain spectroscopy (DTDS) is a new technique that uses pulsed terahertz radiation to characterize the optical properties of thin dielectric films. Characterizing thin films in the GHz to THz range is critical for the development of new technologies in integrated circuitry, photonic systems and micro-electro-mechanical systems. There are potential applications for gene and protein chips. This paper shows how DTDS can be combined with double modulation in the pump-probe system to improve sensitivity by an order of magnitude. An iterative algorithm is presented to estimate the optical properties of a given thin film. The technique is experimentally verified using 1-μm-thick samples of silicon dioxide on silicon.
[show abstract][hide abstract] ABSTRACT: We report the creation of 50 nm thick epitaxial Cu lines with line widths ranging from 20 nm to 120 nm on Si(100) substrate using a combination of electron beam lithography, oblique angle deposition, and lift-off techniques. The increase of measured resistivity as a function of decreasing line width is dominated by surface scattering that is completely diffuse. The measured resistivity of the 20 nm wide lines is ~ 4 μΩ-cm.
Thin Solid Films 07/2012; 520(19):6106–6108. · 1.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: A simple technique is reported to create 31 and 45 μm thick, graded-index Si films in the form of nanospirals on a Si substrate using a dynamic, oblique angle deposition technique. We show that the success in producing such a thick, nanostructured film without delamination from the Si substrate is primarily due to the nano-porous nature of the film which effectively eliminates the stress generated during growth. Effective refractive indices of 1.9 and 2.1 were extracted from the terahertz time-domain reflectivity data, which correspond to 57% and 51% porosity for the 31 and 45 μm thick films, respectively. The gradient of porosity through the film was modeled to describe quantitatively the terahertz reflectance data in the 0.2-2.0 THz regime.
[show abstract][hide abstract] ABSTRACT: Lithium ion batteries are popular for use in portable applications owing to their high energy density. However, with an increasing interest in plug-in hybrid electric vehicles over the past few years, stemming from an urgent need to migrate to green technologies, the focus has shifted to enhancing power densities in Lithium ion batteries. In this review article we focus on some of the recent achievements of the academic and industrial community in boosting the power densities of Lithium ion batteries through the development of novel nanostructured anode and cathode architectures.
[show abstract][hide abstract] ABSTRACT: Vertically aligned, biaxially textured molybdenum nanorods were deposited using dc magnetron sputtering with glancing flux incidence (alpha¼858 with respect to the substrate normal) and a two-step substrate-rotation mode. These nanorods were identified with a body-centered cubic crystal structure. The formation of a vertically aligned biaxial texture with a  out-of-plane orientation was combined with a [-110] in-plane orientation. The kinetics of the growth process was found to be highly sensitive to an optimum rest time of 35 seconds for the two-step substrate rotation mode. At all other rest times, the nanorods possessed two separate biaxial textures each tilted toward one flux direction. While the in-plane texture for the vertical nanorods maintains maximum flux capture area, inclined Mo nanorods deposited at alpha¼858 without substrate rotation display a [-1-1-4] in-plane texture that does not comply with the maximum flux capture area argument. Finally, an in situ capping film was deposited with normal flux incidence over the biaxially textured vertical nanorods resulting in a thin filmover the porous nanorods. This capping filmpossessed the same biaxial texture as the nanorods and could serve as an effective substrate for the epitaxial growth of other functional materials.
Journal of Applied Physics 09/2011; 110(6):064311. · 2.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: Because of the low sticking coefficient, conventional parylene deposition is known to achieve the conformal coating on corrugated or patterned surfaces. However, recently, it has been shown that in contrary to the conformal coating, extremely nonconformal and isolated fibrous parylene structures can be formed on surfaces if it is deposited at an oblique angle using a directional flux. We demonstrate that directional flux can create a high local vapor pressure facing the flux, while the reflection of monomers because of a small sticking coefficient would generate a background vapor pressure. The parylene oblique angle deposition is a combination of the shadowing growth and a much slower conformal coating process, which together give rise to the isolated fibrous structure.
[show abstract][hide abstract] ABSTRACT: Lithium-ion batteries show poor performance for high power applications involving ultrafast charging/discharging rates. Here we report a functionally strain-graded carbon-aluminum-silicon anode architecture that overcomes this drawback. It consists of an array of nanostructures each comprising an amorphous carbon nanorod with an intermediate layer of aluminum that is finally capped by a silicon nanoscoop on the very top. The gradation in strain arises from graded levels of volumetric expansion in these three materials on alloying with lithium. The introduction of aluminum as an intermediate layer enables the gradual transition of strain from carbon to silicon, thereby minimizing the mismatch at interfaces between differentially strained materials and enabling stable operation of the electrode under high-rate charge/discharge conditions. At an accelerated current density of ∼51.2 A/g (i.e., charge/discharge rate of ∼40C), the strain-graded carbon-aluminum-silicon nanoscoop anode provides average capacities of ∼412 mAh/g with a power output of ∼100 kW/kg(electrode) continuously over 100 charge/discharge cycles.
[show abstract][hide abstract] ABSTRACT: The ultraviolet (UV) curable epoxy siloxane polymer is shown to cross-link at low UV dosages of 130mJ/cm2, making it desirable for use in nanoimprinting and the rapid fabrication of micro/nano-scaled patterns. In this paper, the dielectric and mechanical properties of this UV-cured epoxy siloxane polymer are investigated. The results of these tests show that the rapid UV-cured polymer films have a dielectric constant of 2.7±0.13, leakage current density on the order of 10−9A/cm2 under 1MV/cm, dielectric strength of greater than 5MV/cm, and a reduced modulus of elasticity of 6.2GPa characterized using nanoindentation. These properties indicate that the epoxy siloxane can be used to fabricate layers for functional device applications.
Materials Chemistry and Physics - MATER CHEM PHYS. 01/2011; 129(3):678-682.
[show abstract][hide abstract] ABSTRACT: Aluminum has been perceived as a stable electrode for the reliability test of dielectric films. In this letter, using energy dispersive X-ray spectroscopy method, Al ions were detected in the dielectric after Al/SiCOH/SiO2/Si capacitor was subjected to bias-temperature stress (BTS). We investigated the impact of the drifted Al to the stability of the dielectrics by studying the leakage current of the capacitor. We showed that the increase of leakage current after BTS falls into the Poole–Frenkel conduction regime, indicating the Al ions act as electronic traps inside SiCOH. Our results question the compatibility between Al and low-k dielectrics.
[show abstract][hide abstract] ABSTRACT: This article highlights the formation of biaxially textured body centered cubic Mo nanorods under recrystallization conditions using glancing angle deposition. The flux incidence angle has been changed ($alpha$=0°, 70° and 85° away from the surface normal) to observe its effect on the formation of biaxial texture under a constant low Ar pressure environment (0.306 Pa). Only at a glancing flux incidence ($alpha$=85°), the directional diffusion overcomes the effect of recrystallization to yield a highly biaxial texture. In another study, a normal flux incidence ($alpha$=0°) was kept constant and the Ar pressure was changed (0.67, 1.33 and 2.67 Pa) to see its influence on the film morphology and the resulting texture. The Ar pressure variation was aimed at attempting a zone transformation in accordance with the structure zone model. While the morphology appeared to agree with the expected zone transformation, the texture did not.
Thin Solid Films 01/2011; 519(16):5429-5432. · 1.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: Cu penetration into low-k dielectrics can cause serious reliability issues in on-chip interconnect systems. Using secondary ion mass spectrometry with both front-side and back-side depth profiling strategies, Cu was found to diffuse into SiCOH low-k dielectric in a Cu/SiCOH/Si capacitor during Cu deposition. After bias-temperature stressing the capacitor at 270 °C and 2.5 MV/cm, Cu penetrates further into SiCOH, but its distribution profile is the same as that after the same temperature annealing without electrical bias, suggesting no Cu ion drift. The implication of these findings on the Cu/low-k dielectric time-dependent dielectric breakdown modeling is discussed.
[show abstract][hide abstract] ABSTRACT: We report the room temperature growth of biaxially textured Al films and further demonstrate the use of these Al films in preparing single-crystalline Si layers on glass substrates. The formation of the biaxial texture in Al film relies on the existence of the CaF(2) buffer layer prepared using oblique angle physical vapor deposition, which consists of single-crystalline nanorods with caps that are in the form of inverted nanopyramids. The single-crystalline Si film was obtained upon crystallization of the amorphous Si film deposited through physical evaporation on the biaxially textured Al film. This method of preparing single-crystalline Si film on glass substrate is potentially attractive for being employed in silicon technology and in fabrication of low-cost electronic devices.
[show abstract][hide abstract] ABSTRACT: It is known that Ta, a popular diffusion barrier material, can itself penetrate into low- k dielectrics under bias-temperature stress. In this work, we derived a model which directly correlates the diffusivity of Ta ions to the rate of flatband voltage shift (FBS) of the Ta/methyl silsesquixane (MSQ)/Si capacitors. From our experimentally measured constant FBS rate, the Ta diffusivity and activation energy were determined. It appears that an increase in the porosity of MSQ film enhances the Ta diffusivity but does not affect the associated activation energy. This suggests the Ta ion diffusion is mainly through interconnected pore surfaces.
[show abstract][hide abstract] ABSTRACT: Coherent acoustic transport through vertically grown nanorod array on substrate and electron phonon interactions are experimentally studied by using femtosecond laser spectroscopy and glancing angle deposition technique. We have designed a model structure to study the phonon transport along the long axis of nanorods with the use of acoustic spectroscopy. We have experimentally observed the transport of the acoustic pulse with comparable wave length to the diameter of the nanorod, and damping due to the coupling of propagating acoustic phonon to the eigen mode of nanorod (bending motion). Electron-phonon interaction in copper nanorod arrays was studied using ultrafast transient reflectivity spectroscopy with both resonant and off-resonant probe to d-band to Fermi-level transition. Slanted nanorod arrays 10 nm - 50 nm in diameter were fabricated by newly developed deposition technique. The use of a variable probe wavelength over the transition energy range suggested the modification of electronic structure in slanted nanorod arrays with relatively large diameter.
[show abstract][hide abstract] ABSTRACT: We report the investigation of a novel microfluidic mixing device to achieve submillisecond mixing. The micromixer combines two fluid streams of several microliters per second into a mixing compartment integrated with two T- type premixers and 4 butterfly-shaped in-channel mixing elements. We have employed three dimensional fluidic simulations to evaluate the mixing efficiency, and have constructed physical devices utilizing conventional microfabrication techniques. The simulation indicated thorough mixing at flow rate as low as 6 µL/s. The corresponding mean residence time is 0.44 ms for 90% of the particles simulated, or 0.49 ms for 95% of the particles simulated, respectively. The mixing efficiency of the physical device was also evaluated using fluorescein dye solutions and FluoSphere-red nanoparticles suspensions. The constructed micromixers achieved thorough mixing at the same flow rate of 6 µL/s, with the mixing indices of 96% ± 1%, and 98% ± 1% for the dye and the nanoparticle, respectively. The experimental results are consistent with the simulation data. The device demonstrated promising capabilities for time resolved studies for macromolecular dynamics of biological macromolecules.
Sensors and Actuators B Chemical 01/2010; 144(1):301-309. · 3.54 Impact Factor
[show abstract][hide abstract] ABSTRACT: The degradation of conjugated polymer poly(p-phenylene vinylene) (PPV) in the atmosphere upon exposure to ultraviolet light limits its applications as the emitting layer in organic light emitting diodes. In this paper we show that a thin layer of aluminum oxide around 10nm in thickness prevents photoluminescence degradation of PPV during exposure to blue light in the atmosphere but not at lower excitation wavelengths. This oxide film is free of cracks and pinholes from transmission electron microscopy analysis.
Thin Solid Films 01/2010; 518(15):4367-4369. · 1.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: Amorphous carbon films were deposited successfully on Cu foils by DC magnetron sputtering technique. Electrochemical performance of the film as lithium battery anode was evaluated across Li metal at 0.2C rate in a non-aqueous electrolyte. The discharge curves showed unusually low irreversible capacity in the first cycle with a reversible capacity of ∼810mAhg−1, which is at least 2 times higher than that of graphitic carbon. For the first time we report here an amorphous carbon showing such a high reversibility in the first cycle, which is very much limited to the graphitic carbon. The deposited films were extensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and step profilometer for the structural and surface properties. The hydrogen content of the synthesized films was studied using residual gas analysis (RGA). The low hydrogen content and the low specific surface area of the synthesized amorphous carbon film are considered responsible for such a high first cycle columbic efficiency. The growth mechanism and the reasons for enhanced electrochemical performance of the carbon films are discussed.
Journal of Power Sources 01/2010; 195(7):2044-2049. · 4.68 Impact Factor