Nano-thick Films Research Articles

A novel approach of using a MBE template for ALD growth of high- κ dielectrics

We have employed molecular beam epitaxy (MBE) to grow high κ dielectric nano-thick films of Al 2O 3 and HfO 2 on Si (1 0 0) as templates to suppress effectively the formation of the oxide/Si interfacial layer during the subsequent atomic layer deposition (ALD) growth for Al 2O 3. We show marked improvements of electrical performance of the ALD+MBE composite oxides. A first bi-layer composite of ALD Al 2O 3 1.9 nm/MBE Al 2O 3 1.4 nm showed a dielectric constant of 9.1 with an equivalent oxide thickness (EOT) of 1.41 nm. The interfacial trap density D it was 2.2×10 11 cm −2 eV −1 as deduced from the conductance method, with the leakage current density being 2.4×10 −2 A/cm 2 at V fb−1 V. The second bi-layer of ALD Al 2O 3 3.0 nm/MBE HfO 2 2.0 nm showed a dielectric constant of 11.5 and an EOT of 1.7 nm. The D it was estimated to be 2×10 11 cm −2 eV −1 with the leakage being 1.1×10 −4 A/cm 2 at V fb+1 V.

Carrier carrying capacity of one-step grown suspended carbon nanotube bridge with carbon nanotube contact electrodes: For practical one-dimensional electronics

The authors report the carrier transport and electrical breakdown behaviors of micron-long-channel suspended carbon nanotube (CNT) of carbon-based one-dimensional junction with CNTs as drain and source electrodes. The structure consisted of bundle-type CNT electrode–a CNT channel–bundle-type CNT electrode, produced by one-step in situ direct growth via a unique diluted magnetic nanothick film catalyst at low temperature. The unique suspended all-one-dimensional CNT-based junction provides some insights into recent reports that an electrical breakdown of CNTs can be induced not by the contact problem but by the nonhomogeneously Joule heating along nanotube without release of heat into contacts by the observed breakdown at midlength of a 1–2μm long channel. The high current carrying all-CNT junction with bridging yield of 90% and stable operation at fixed voltage level can contribute into realization of practical integrated nanoelectronics such as interconnector and transistor via junction formation of one-step final process.

Indentation testing of axisymmetric freestanding nanofilms using a MEMS load cell

We have developed a new scientific tool for the mechanical characterization of axisymmetric freestanding nano-thickness films. The tool consists of a calibrated MEMS-based load cell with a spherical loading tip, and a positioning system capable of sub-nm accuracy. The loading tip is positioned over the center of a free-standing film using a two-axis positioning stage. A Michelson Interferometer is positioned below the film to record the displacement field of the membrane, in situ, as the load cell deflects the membrane from above. As the MEMS load cell is lowered into the axisymmetric freestanding thin film, concentric fringes emanate from the center of the thin film sample. This tool allows us to record the applied load and membrane displacement simultaneously. To date, load cells with stiffnesses as low as 2 nN/μm have been fabricated and calibrated. We have validated the operation of the apparatus using gold films 1080 μm in diameter and 170 nm thick.

나노두께 퍼말로이에서의 계면효과에 의한 자기적 물성 변화

나노 두께의 NiFe의 자기적 특성을 살펴보기 위해 Si(100)/ <TEX>$SiO_2$</TEX>(200 nm)/Ta(5 nm)/N <TEX>$i_{80}$</TEX>F <TEX>$e_{20}$</TEX>(1～15 nm)의 구조를 ICP형 헬리콘 스퍼터로 제작하였다. 제작된 시편의 자기적 물성은 SQUID를 이용하여 <TEX>$\pm$</TEX>50 Oe에서의 4.2K와 300K에서 각각의 M-H loop를 측정하여 자기탄성에너지 변화와 보자력을 확인하였다. 또한 SQUID로 4.2K-300K에서의 M-T curve를 통해 온도에 따른 포화자화를 두께에 따라 살펴보았다. TEM을 사용하여 제작된 시편의 각 계면간의 미세구조를 살펴보았다 나노두께의 NiFe는 3 nm 이하에서는 <TEX>$B_{bulk}$</TEX>=0, <TEX>$B_{surf}$</TEX>=-3<TEX>${\times}$</TEX><TEX>$10^{-7}$</TEX>(J/<TEX>$m^2$</TEX>)의 자기 탄성계수를 보였으며, 보자력은 급격히 증가하는 것을 확인하였다. 나노 두께의 퍼말로이는 계면효과에 의해서 벌크특성과 다른 자기탄성계수, 보자력, Ms의 변화가 발생하였다. 따라서 나노급 소자를 제작할 때 이러한 변화를 고려하여 설계하여야 하였다. We prepared ultra thin film structure of Si(100)/ <TEX>$SiO_2$</TEX>(200 nm)/Ta(5 nm)/Ni<TEX>$_{80}$</TEX>Fe<TEX>$_{20/(l～15 nm)}$</TEX>Ta(5 nm) using an inductively coupled plasma(ICP) helicon sputter. Magnetic properties and cross-sectional microstructures were investigated with a superconduction quantum interference device(SQUID) and a transmission electron microscope(TEM), respectively. We report that NiFe films of sub-3 nm thickness show the B<TEX>$_{bulk}$</TEX> = 0 and B<TEX>$_{surf}$</TEX>=-3 <TEX>${\times}$</TEX> 10<TEX>$^{-7}$</TEX>(J/<TEX>$m^2$</TEX>). Moreover, Curie temperature may be lowered by decreasing thickness. Coercivity become larger as temperature decreased with 0.5 nm - thick Ta/NiFe interface intermixing. Our result implies that effective magnetic properties of magnetoelastic anisotropy, saturation magnetization, and coercivity may change abruptly in nano-thick films. Thus we should consider those abrupt changes in designing nano-devices such as MRAM applications.

Fabrication and nonlinear optical properties of ultrathin films containing sulfonate functionalized fullerenes

An ultrathin composite film containing both poly(diallyldimethyl ammonium chloride) (PDDA) and hexa(sulfobutyl)fullerenes (C 60-HS) has been fabricated by the electrostatic layer-by-layer self-assembly technique. UV–Vis spectra showed a continuous deposition process of PDDA and C 60-HS. The film structure was characterized by small angle X-ray diffraction measurement and AFM image. The nanothick film showed an effective third-order nonlinear refractive index n 2=1.56×10 −8 esu.

Preparation and nonlinear optical properties of ultrathin composite films containing both a polyoxometalate anion and a binuclear phthalocyanine

An ultrathin composite film containing both polyoxometalate anion [PMo12O40]3− (PMo12) and a planar binuclear phthalocyanine, bi-CoPc, has been prepared by the electrostatic layer-by-layer self-assembly method. UV-vis measurements revealed regular film growth with each four-layer {PMo12/bi-CoPc/PSS/PAH} adsorption. The film structure was characterized by small-angle X-ray reflectivity measurements, X-ray photoelectron spectra, and AFM images. The nanothick film shows a third-order nonlinear optical response of χ(3) = 4.21 × 10−12 esu. Experimental investigations also indicate that the combination of polyoxometalate anions [PMo12O40]3− with the phthalocyanine bi-CoPc in multilayer films can enhance the third-order NLO susceptibility and modify the third-order NLO absorption of bi-CoPc.

Applications of atomic layer chemical vapor deposition for the processing of nanolaminate structures

Atomic layer chemical vapor deposition (ALCVD) is a variant of a CVD process that involves surface deposition for the controlled growth of nano-thickness films. ALCVD is based on the self-limiting surface reaction with less than a monolayer chemisorption of chemical precursors. Advantages of the ALCVD process are uniform film growth on large area substrate, easy control of composition in atomic level, low growth temperature, multi-layer thin film growth with various composition, and wide process window. Since initially developed by Suntola in 1977, ALCVD has been used for the growth of various materials, including oxides, nitrides, metals, elements, and compound semiconductors. This article reviews the basic principle, mechanism, characteristics, and applications of ALCVD.

Preparation of titanium dioxide and barium titanate nanothick film by Langmuir–Blodgett technique

The TiO 2 and BaO(TiO 2) x thin film was prepared by the Langmuir–Blodgett (LB) technique. The mixture of octadecyl polymaleicate and tetrabutoxytitanium was spread on the surface of water subphase, then transferred onto substrates. The obtained LB multilayer was converted into a nano-thick TiO 2 film by calcination at 500°C for 30 min. When an appropriate amount of BaCl 2 was added into a water subphase, it was co-transferred onto a LB multilayer film. After calcination at the same condition, BaO(TiO 2) x thin films with different ratios of x could be obtained by adjusting the pH value of the water subphase. The Fourier transform infrared spectroscopy and X-ray photoelectron spectra measurements were used to confirm the formation of TiO 2 and BaO(TiO 2) x thin films. The integrated peak area in X-ray photoelectron spectra gave the atomic ratio of Ti/O and Ti/Ba. The surface morphology of the LB multilayer before and after calcination was investigated by atomic force microscopy. The image showed that the smooth and high cover surface of TiO 2 and BaO(TiO 2) x thin films were obtained after calcination. The rms roughness for a 21-layer film after calcination was approximately 25 Å, which was less than that of before calcination of approximately 45 Å. The resulting particle size was approximately 0.05 μm and almost uniform.

Control of particle adhesion to surfaces by depositing nanometric interfacial layers

ABSTRACTThe influence of nano-thick hydrophilic or hydrophobic films on adhesion properties of particles to surfaces has been investigated. Al2O3 and Ag layers were deposited on Ag and Al2O3 core particles, respectively by a modification of pulsed laser deposition technique. The as-received and surface-modified particles were further coated by a secondary process with submicron Al2O3 particles. We observe that deposition of hydrophobic or hydrophilic surfaces affects the surface coverage of secondary particles on core particles and hence the adhesion characteristics.