ICMCTF2011 Session F1-2: Nanomaterials, Nanofabrication, and Diagnostics

Thursday, May 5, 2011 1:30 PM in Room Sunset
Thursday Afternoon

Time Period ThA Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF2011 Schedule

Start Invited? Item
1:30 PM F1-2-1 Fabrication of Aluminum Nanodot Assisted Growth of Nanoroots for Application in Amorphous/Crystalline Silicon Composite Thin Film Solar Cells
Benjamin Newton, Hafeezuddin Mohammed, Husam Abu-Safe, ShuiQing Yu, Hameed Naseem (University of Arkansas)
The high absorption coefficient of amorphous silicon and the superb transport properties of crystalline silicon are combined in a newly proposed composite thin film solar cell comprising of crystalline nanoroots formed by metal nanodot assisted crystallization of amorphous silicon. The nanodots and nanoroots enhance light trapping through surface plasmon generation and absorption for highly stable low cost high efficiency solar cells. Aluminum nanodots were created utilizing a standardized method of deposition through an array of nanometer holes created in a sacrificial silicon dioxide template that was deposited onto a film of amorphous silicon. Aluminum was then deposited using sputtering on an amorphous silicon film supported on a <100> crystalline silicon substrate. The aluminum nanodots were then annealed at temperatures ranging from 200 to 450°C. The growth characteristics of nanoroots were analyzed using ESEM and TEM.
1:50 PM F1-2-2 Platinum Doped Molybdenum Oxide Nanowires Alcohol Gas Sensor by Atomic Layer Deposition
Chen-Chuan Chang (National Tsing Hua University, Taiwan); Han-Chang Shih (Chinese Culture University, Taiwan)

The molybdenum trioxide (MoO3) nanowires were prepared by thermal chemical vapor deposition through a two-step evaporation process and distributed on a p-type Si (100) substrate from molybdenum trioxide powders at 900oC. These obtained nanowires were deposited the platinum nanoparticles by atomic layer deposition (ALD), the morphology, crystal and alcohol gas sensing properties of undoped and platinum doped MoO­3 nanowires were investigated. The MoO3 nanowires were rod-like shape and the diameter were approximately 10-500 nm and several hundreds of nanometers in length. Gas sensors base on updoped, 0.5 wt% and 1.0 wt% platinum-doped MoO3 were fabricated. The MoO­­3 nanowire gas sensor showed a reversible response to alcohol gas at an operating temperature of RT-250oC. The sensor response increased with increasing Pt concentration. The results demonstrated that Pd doping improved the sensor response and lowered the operating temperature at which the sensor response was maximized.

2:10 PM Invited F1-2-3 Nanorods, Nanopipes, Nanosmiles
Daniel Gall (Rensselaer Polytechnic Institute)
Atomic shadowing during physical vapor deposition causes exacerbated growth of surface protrusions and leads to a chaotic 3D layer growth, which can result in the development of well-separated nanorods, nanosprings, or nanopipes, which are surprisingly regular and have potential applications ranging from fuel cell electrodes and pressure sensors to self-lubricating coatings and nanoactuation. Glancing angle deposition (GLAD) causes particularly strong atomic shadowing and can be used to systematically investigate the effect of shadowing on the morphological evolution. These extremely rough layers cannot be described as a chaotic perturbation from a flat surface. However, using a model which describes them as a nanorod array with an average rod width that follows power law scaling results in experimental curves where all metals converge on a single master curve which exhibits a discontinuity at 20% of the melting point, associated with a transition from a 2D to a 3D island growth mode, and a single homologous activation energy of 2.46 for surface diffusion on curved nanorod growth fronts, which is applicable to all metals at all temperatures. Also, under extreme shadowing conditions, the conventional structure zone model is simplified as there is a direct transition from an underdense (zone I) to a dense (zone III) structure at ~50% of the melting point.
2:50 PM F1-2-5 Effects of Temperature and Pulse Mode on Nanoporous Anodic Aluminum Oxide Film by Potentiostatic Anodization
Chen-Kuei Chung, Ming-Wei Liao, Hao-Chin Chang (National Cheng Kung University, Taiwan)
Conventional anodic aluminum oxide (AAO) templates were performed using potentiostatic method of direct current anodization (DCA) at low temperature (0-10°C) to avoid dissolution effect. Recently, pulse anodization (PA) has been used to improve quality of AAO films and we have demonstrated the reversed current occurred randomly from PA approach could be effectively suppressed by hybrid pulse anodization (HPA) at room temperature. In this article, the effects of temperature and pulse mode on AAO films have been investigated in terms of joule heat and burning phenomenon. Two-step anodization in 0.3 M oxalic acid was performed for fabricating AAO films by different pulse modes of HPA, PA and DCA at temperatures of 5-25°C. In addition, the voltage was applied in the range of 30-40 V in order to further verify effect of pulse modes. The morphology, pore size and oxide thickness of AAO films were characterized by high resolution field emission scanning electron microscope (HR-FESEM). The pore size distribution of AAO films can be quantitative analyzed by image processing from SEM images. The uniformity of nanopore size distribution by HPA is better than PA and DCA at relatively high room temperature due to the low joule heat to diminish the dissolution of burning. The pore size of AAO films is related to temperature and voltage and used for varied nanostructure application.
3:10 PM F1-2-7 Epitaxial Si Layer Formed on ZrB2 Thin Films - Silicene?
Antoine Fleurence, Rainer Friedlein, Ying Wang, Fabio Bussolotti, Yukiko Yamada-Takamura (School of Materials Science, JAIST, Japan)

Silicene, which is a two-dimensional sheet of silicon, is increasingly attracting interests owing to the success of graphene - its carbon counterpart. Similarly, massless fermions may occur as suggested in a recent theoretical study [1]. Here, we demonstrate that a two-dimensional, ordered Si layer can be prepared through surface segregation on a metallic film grown epitaxially on Si(111).

Zirconium diboride (ZrB2) is a metallic ceramics with a high melting point. Thin films with a high purity and crystallinity can be grown on Si(111) through thermal decomposition of Zr(BH4)4 molecules under optimized conditions [2]. We have recently obtained predominantly single-crystalline films [3] with an epitaxial relationship of ZrB2(0001)//Si(111) and ZrB2[1-100]//Si[11-2]. Natural oxides formed on the film upon exposure to air could be removed by heating in ultrahigh vacuum. The oxide-free film surface shows a ZrB2(0001)-(2×2) reconstruction. Scanning Tunneling Microscopy (STM) imaging on this surface shows that the atomically-flat ZrB2(0001) terraces are uniformly covered with periodic stripes of two types of (2×2) domains having domain boundaries along ZrB2<11-20> directions and domain width equivalent to four to five (2×2) half unit cells. The observation of Zr-related surface states by Angle-Resolved Ultraviolet Photoelectron Spectroscopy (ARUPS) proofs that the top-most hexagonal close-packed Zr layer remains intact in spite of the (2×2) reconstruction [3]. Both Zr- and Si-related electronic states follow the (2×2) symmetry showing that the electronic subsystems are not independent from each other. Surface-sensitive core-level photoelectron spectroscopy performed using a photon energy of 130 eV identifies Si atoms in different chemical states that are either in contact with Zr atoms or not. Further details of the relationship between the electronic structure of this epitaxial Si layer on metallic ZrB2(0001) thin film and the atomistic structure will be discussed.

References:

[1] S. Cahangirov, M. Topsakal, E. Aktuerk, H. Sahin, and S. Ciraci, Phys. Rev. Lett. 102, 236804 (2009).

[2] C. W. Hu, A. V. G. Chizmeshya, J. Tolle, J. Kouvetakis, and I. S. T. Tsong, J. Cryst. Growth 267, 554 (2004).

[3] Y. Yamada-Takamura, F. Bussolotti, A. Fleurence, S. Bera, and R. Friedlein, Appl. Phys. Lett. 97, 073109 (2010).
3:30 PM F1-2-8 Synthesis of Bioactive NaHTi3O7 Films on Ti-Coated Si by a Hydrothermal - Galvanic Couple Method
Chia-Jung Yang, Ling-Su Chao (National Chung Hsing University, Taiwan); Yu-Chih Chieh (Hsiuping Institute of Technology, Taiwan); Fu-Hsing Lu (National Chung Hsing University, Taiwan)
The bioactive NaHTi3O7 films were synthesized on Ti-coated Si substrates below 100oC by a novel hydrothermal-galvanic couple (HT-GC) method. A hydrothermal (HT) method was also conducted for comparison. The thickness of obtained NaHTi3O7 films synthesized by the HT-GC method was much higher than that prepared by the HT method in 4M NaOH solutions at 80oC for 2hr. This indicates that the hydrothermal method aided by a galvanic couple setup could enhance significantly the growth rate of the films. The obtained NaHTi3O7 films exhibited nano-network structures and their pore sizes within the network increased with the NaOH concentration and the reaction temperature, as well as the reaction time . I n simulated body fluid solutions, calcium phosphate-based products were formed on the NaHTi3O7 films, suggesting that the films have great potentials in biomaterial applications.
3:50 PM F1-2-9 Amorphous Phases and Crystallization Behaviour of Sputtered Fe1-xCx Films with x Ranging between 0.32 and 0.50
Elizabeth Bauer-Grosse (Nancy-University, France); Gerard Le Caër (Universite de Rennes, France)

Iron-carbon and iron-carbon based alloys , which are of great importance from both fundamental and applied points of view, have triggered a wealth of publications which are most often devoted to studies of crystalline alloys with nanosized, ultra-fine or micron-sized grains. A full knowledge of the Fe-C system requires further to investigate and characterize amorphous Fe-C alloys which are known to exist in a wide concentration range. Sputtered Fe1-xCx amorphous films were for instance found to exist for a carbon content x ranging between 0.19 and 0.50. These amorphous alloys can be prepared either as thin films or as powders, for instance when they are synthesized by mechanical alloying. The Fe-C amorphous alloys are interesting in their own for their peculiar structure, which depends on the carbon content, and for their intrinsic physical properties. Further, they are sources of new metastable carbides which are formed during their crystallization. The present work addresses the characterization of the carbon-richest Fe1-xCx films (x > 0.32) with a special attention dedicated to Fe0.55C0.45. Electron probe microanalysis was used to determine the carbon content. As-sputtered amorphous films were characterized by Mössbauer spectrometry, X-ray and/or electron diffraction. Their thermal stability was studied by differential scanning calorimetry. The products of crystallization were identified both from Mössbauer spectra and from X-ray diffraction patterns. Crystallization was followed in situ using a hot stage transmission electron microscopy. For any carbon content in the range 0.32-0.50, the Mössbauer hyperfine parameters are observed to remain constant while the main crystallization product is identified to be the Fe7C3 carbide. These results indicate that, for x > 0.32, the amorphous films are composed of two phases: one Fe-rich metallic Fe-C phase, with a carbon content close to 0.3, and an amorphous carbon phase deprived of iron. The composition of the metallic phase remains essentially constant when the carbon content increases. Then, it is the increase of the fraction of the amorphous carbon phase which accomodates the carbon content increase. According to the carbon content, amorphous Fe-C films may be looked at as nanocomposites formed by two components, a metallic amorphous one and an amorphous carbon one, whose proportions can be controlled by a choice of the carbon content.

4:10 PM F1-2-11 Frost Reduction on the Micro/Nano Structured Superhydrophobic Aluminium Surface
Chin-Ting Yang, Chih-Hao Lan (St. John's University, Taiwan)

In refrigeration system, the heat transfer performance of evaporator is decreased when the fins covered with frost. The defrosting process is time and energy consumptions. The modification of superhydrophobic thin film on the aluminum fin surface could prevent the condensate water drop staying on the surface and so reduce the frost deposition. In order to modify the aluminum surface to be superhydrophobic, a thin film of micro/nano structure was coated by sol-gel process. The Tetraethoxysilane(TEOS) and Methyltrimethoxysilane (METMS) were employed and mixed with micro/nano silica particles to function like the lotus leaf. Those silane couple agents also provided the bonding force between aluminum and silica particles. The water contact angle of original untreated aluminum surface is 85 degrees. The best one after modification can reach 163 degrees. The SEM images tell that the more nano particles used, the more roughness the surface was, which the contact angle enhancement can be explained by Cassie-Baxter model. In order to understand how the wettability affects the frost deposition, the aluminum plate samples were placed in the refrigerator cold chamber and hot water was used to speed up the frosting process. After a period of time the samples were weighed by digital scale. The results show that the higher contact angle the surface had, the less frost deposition on surface happened. Compare to untreated aluminum plate, the frost deposition is only half when the contact angle is 163 degrees. For the long term (7 hours) frosting running, the frost reduction ability is decreased. Because when the superhydrophobic film was covered with frost, the high contact angle state cannot persist.

4:30 PM F1-2-12 Micro/Nanostructured Surfaces of a-C:H:F Films with Anisotropic Properties
Carles Corbella, Victor-Manuel Freire, Sabine Portal, Gerard Oncins, Enric Bertran, José-Luis Andújar (Universitat de Barcelona, Spain)
Amorphous hydrogenated carbon films with fluorine (a-C:H:F) with special surface properties have been fabricated by combining lithography techniques and plasma deposition. First, silicon wafers were patterned either by laser lithography or by colloidal lithography with silica nanospheres. Both techniques generated micro/nanotextures showing in-plane anisotropy on the surface. After that, the samples were coated by a-C:H:F thin films by pulsed-DC plasma-enhanced chemical vapor deposition using CH4 and CHF3 as precursors. Structural and morphological studies were carried out by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface properties evidenced the formed anisotropy, as shown by the directional dependences of wettability and friction coefficient. Wettability, which was measured by water contact angle, showed an anisotropic chararacter evidenced by the elongated shape of the wetting drops. Superhydrophobicity was achieved on the preferential direction of the pattern. The tribological properties of the samples were also influenced by the in-plane anisotropy, as measured with a nanotribometer and an AFM operating in contact mode. Differences in friction coefficient and wear rate as a function of scan direction, load and contact area are discussed. Silica nanoparticles were arranged on the micropatterns to test their performance as self-assembly surfaces. These samples find applications where hard coatings with anisotropic properties are required, e.g. microelectromechanical devices (MEMs), microfluidics and patterned surfaces for biomedicine.
4:50 PM F1-2-13 Correlation Between Plasma and Properties of Cr2AlC MAX Phase Coatings
Christoph Leyens, Olaf Schroeter, Rajorshi Basu (Technische Universität Dresden, Germany)

Cr2AlC has recently been studied as a MAX phase coating due to its excellent thermo-mechanical properties resulting from its inherent nano-laminated structure. In the present paper the correlation between plasma characteristics during sputtering and the resulting coating properties will be shown. A sintered Cr2AlC powder target was used for high power impulse magnetron sputtering (HIPIMS) or conventional DC magnetron sputtering. HIPIMS sputtering was performed at different pressures and at different pulse power levels; the effect of process parameters on the plasma was investigated by a quadrupole mass spectrometer. Plasma composition as well as amount and energies of single and double charged ions were analyzed. Moreover, the structure, the morphology and selected properties of the coatings were investigated. The Cr2AlC coatings were single MAX phase; coating morphology and internal stress state were varied by using different bias voltages. Depending on the process parameters, the Cr2AlC MAX phase coatings showed high adhesion in scratch test and very good plastic performance.

Time Period ThA Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF2011 Schedule