Kunbae Noh

Extreme superomniphobicity of multiwalled 8 nm TiO2 nanotubes.

We report unprecedented superomniphobic characteristics of nanotube-structured TiO(2) surface fabricated by electrochemical etching and hydrothermal synthesis process, with the wettability contact angles for water and oil both being ∼174° or higher. A tangled forest of ∼8-nm-diameter, multiwalled nanotubes of TiO(2) was produced on the microtextured Ti surface, with the overall nanotube length controlled to 150 nm by adjusting the processing time. Wettability measurements indicate that the nanotube surface is extremely nonwettable to both water and oil. The contact angle of the 8 nm TiO(2) nanotube surface after perfluorosilane coating is extremely high (178°) for water droplets indicating superhydrophobic properties. The contact angle for oil, measured using a glycerol droplet, is also very high, about 174°, indicating superoleophobic characteristics. These dual nonwetting properties, superomniphobic characteristics, are in sharp contrast to the as-made TiO(2) nanotubes which exhibit superhydrophilic properties with a contact angle of essentially ∼0°. Such an extreme superomniphobic material made by a simple and versatile method can be useful for a variety of technical applications. It is interesting to note that all three properties can be obtained with identical nanotube structures. A nanometer-scaled structure introduced by hydrothermally grown TiO(2) nanotubes is an effective air trapping nanostructure in enhancing the amphiphobic (superomniphobic) wettability.

Tantalum coating on TiO2 nanotubes induces superior rate of matrix mineralization and osteofunctionality in human osteoblasts

Nanostructured surface geometries have been the focus of a multitude of recent biomaterial research, and exciting findings have been published. However, only a few publications have directly compared nanostructures of various surface chemistries. The work herein directly compares the response of human osteoblast cells to surfaces of identical nanotube geometries with two well-known orthopedic biomaterials: titanium oxide (TiO2) and tantalum (Ta). The results reveal that the Ta surface chemistry on the nanotube architecture enhances alkaline phosphatase activity, and promotes a ~30% faster rate of matrix mineralization and bone-nodule formation when compared to results on bare TiO2 nanotubes. This study implies that unique combinations of surface chemistry and nanostructure may influence cell behavior due to distinctive physico-chemical properties. These findings are of paramount importance to the orthopedics field for understanding cell behavior in response to subtle alterations in nanostructure and surface chemistry, and will enable further insight into the complex manipulation of biomaterial surfaces. With increased focus in the field of orthopedic materials research on nanostructured surfaces, this study emphasizes the need for careful and systematic review of variations in surface chemistry in concurrence with nanotopographical changes.

Preparation of near micrometer-sized TiO2 nanotube arrays by high voltage anodization.

Highly ordered TiO2 nanotube arrays with large diameter of 680-750 nm have been prepared by high voltage anodization in an electrolyte containing ethylene glycol at room temperature. To effectively suppress dielectric breakdown due to high voltage, pre-anodized TiO2 film was formed prior to the main anodizing process. Vertically aligned, large sized TiO2 nanotubes with double-wall structure have been demonstrated by SEM in detail under various anodizing voltages up to 225 V. The interface between the inner and outer walls in the double-wall configuration is porous. Surface topography of the large diameter TiO2 nanotube array is substantially improved and effective control of the growth of large diameter TiO2 nanotube array is achieved. Interestingly, the hemispherical barrier layer located at the bottom of TiO2 nanotubes formed in this work has crinkles analogous to the morphology of the brain cortex. These structures are potentially useful for orthopedic implants, storage of biological agents for controlled release, and solar cell applications.

Hybrid micro/nano-topography of a TiO2 nanotube-coated commercial zirconia femoral knee implant promotes bone cell adhesion in vitro.

Various approaches have been studied to engineer the implant surface to enhance bone in-growth properties, particularly using micro- and nano-topography. In this study, the behavior of osteoblast (bone) cells was analyzed in response to a titanium oxide (TiO2) nanotube-coated commercial zirconia femoral knee implant consisting of a combined surface structure of a micro-roughened surface with the nanotube coating. The osteoblast cells demonstrated high degrees of adhesion and integration into the surface of the nanotube-coated implant material, indicating preferential cell behavior on this surface when compared to the bare implant. The results of this brief study provide sufficient evidence to encourage future studies. The development of such hierarchical micro- and nano-topographical features, as demonstrated in this work, can provide insightful designs for advanced bone-inducing material coatings on ceramic orthopedic implant surfaces.

An X–Y Addressable Matrix Odor‐Releasing System Using an On–Off Switchable Device

In recent decades, much research has been dedicated to the development of virtual reality for entertainment, engineering, and medical application. Virtual reality can be made more realistic with an artificial three-dimensional visual or other sensory environment using the experience of moving seats, odors of explosives or flowers, sprinkling water, laser lights, and wind blowing. Odor-releasing devices that allow repeatable, remote, and reliable switching of odor flux, in particular, could have a significant impact on the effectiveness of virtual reality. However, although various devices for the added sense experience have been developed recently, very few odor-generating devices with practical and useful control of induced sense of smell have been reported. The development of an odor-releasing system that can provide specific odor selectively began in the early days as a crude device. The oldest system is “Sensorama”, a game machine, wherein odor is presented according to the scene on the display and the chair or steering wheel vibrates. After Sensorama, there were discussions about which movie needs odor presentation, referring to some experiments on providing odors synchronously as the movie scenes evolve. In the AMLUX theatre, there was an attempt to add odor information to visual media. Also, there have been some tests to induce the relaxation effect through odor presentation in art objects. Furthermore, there were some approaches to utilize odor information for the fire-fighter training system, and the soldier training system by using a scent collar. These systems present odor information by evaporating bulk smelly material or by spraying it using propellant gas or inkjet technology. However, these well-known technologies are coarse and crude in nature, and it is hard to apply them to delicate home electronics or personal devices owing to their bulkiness, their lack of reproducible release over multiple cycles, their slow response times to stimuli, as well as their inability to dynamically adjust the amount/intensity of odor according to the recipient s needs. Therefore, the development of odorreleasing or transferring systems for the electronic device virtual reality has been difficult. Moreover, televisions, hometheatre, or video-game devices are getting thinner and smaller, requiring faster and more accurate control. Indeed, no existing device could overcome all of these limitations at the moment. For example, an automatic aerosol dispenser containing odor-filled reservoirs can achieve rapid on-demand odor delivery but the odor-storing cans are filled with compressed gas or flammable solvents used as propellants and require a complicated valve system which is difficult to scale down. The desirable odor-generating systems should not depend on a mechanical switching system and should be thin enough to insert into small devices. For these reasons, innovative technologies are needed. The primary requirement to the development of a gas-release device for odor generation is an accurate control capability. From this perspective, an ideal device for odor generation should safely contain a suitable quantity of odor-releasable solution, can release little or no odor in the “off” state, and be repeatedly switched to the “on” state without mechanically disrupting the device. In recent years, many researchers have been trying to develop on–off switchable devices for drug release using polymers, because some polymers have good reversible switching properties. We have employed in our new odorgenerating system, a stable polymer, polydimethylsiloxane (PDMS), a representative silicone elastomer. PDMS is optically clear and, in general, is considered to be inert, non-toxic, and non-flammable. One of the primary fields of applications for PDMS is the embedding or encapsulation of electronic components by casting, which prolongs the lifespan of the circuit chips. A silicone elastomer such as PDMS, exhibits mechanical elasticity, acts as a dielectric isolator, and protects the components from environmental factors and mechanical shock over a relatively large temperature span (e.g., 50–200 8C). In addition, the inertness and stability of PDMS has been traditionally utilized as a biomaterial in implants, catheters, drainage tubing, and membrane oxygenators. We have therefore utilized the desirable properties of PDMS for the development of our on–off switchable odor releasing system. Cross-linked (cured) PDMS elastomer does not allow aqueous solvents to infiltrate and swell the polymer, so that it can be used as a container which can store a water-based liquid. Although elastomers are not [*] H. Kim, K. Noh, C. J. Gardner, Dr. S. D. Kong, Prof. Dr. S. Jin Materials Science and Engineering University of California, San Diego 9500 Gilman Drive, La Jolla, CA 92093-0411 (USA) Fax: (+ 1)858-534-5698 E-mail: jin@ucsd.edu Homepage: http://maeweb.ucsd.edu/~ jin/ Dr. J. Park, Dr. J. Kim Samsung Advanced Institute of Technology, Frontier Research Lab Samsung Electronics Co., Ltd. Suwon, Gyeonggi-Do 443-742 (Korea) Fax: (+ 82)31-280-9349 E-mail: jongkim@samsung.com [] These authors contributed equally.

GUIDED NANOSTRUCTURES USING ANODIZED ALUMINUM OXIDE TEMPLATES

In this paper, we review recent advances in nanotemplate fabrication using anodized aluminum oxide (AAO). In addition to self-ordered AAO nanoarrays, guided AAO self-assembly is of great interest since it can offer highly ordered, vertically aligned nanoporous templates which are suitable for various materials synthesis and alignment of nanosized structures. Moreover, structural modification of AAO nanoarrays by controlling fabrication process parameters are reviewed which can be applicable for advanced micro- and nanosystems. In this aspect, potential applications using AAO will be revealed in the aspects of self-ordered AAO, guided self-assembly of AAO, and biomedical and magnetic applications.

Unusually High Optical Transparency in Hexagonal Nanopatterned Graphene with Enhanced Conductivity by Chemical Doping

Graphene has received appreciable attention for its potential applications in flexible conducting film due to its exceptional optical, mechanical, and electrical properties. However increasing transmittance of graphene without sacrificing the electrical conductivity has been difficult. The fabrication of optically highly transparent (≈98%) graphene layer with a reasonable electrical conductivity is demonstrated here by nanopatterning and doping. Anodized aluminium oxide nanomask prepared by facile and simple self-assembly technique is utilized to produce an essentially hexagonally nanopatterned graphene. The electrical resistance of the graphene increases significantly by a factor of ≈15 by removal of substantial graphene regions via nanopatterning into hexagonal array pores. However, the use of chemical doping on the nanopatterned graphene almost completely recovers the lost electrical conductivity, thus leading to a desirably much more optically transparent conductor having ≈6.9 times reduced light blockage by graphene material without much loss of electrical conductivity. It is likely that the availability of large number of edges created in the nanopatterned graphene provides ideal sites for chemical dopant attachment, leading to a significant reduction of the sheet resistance. The results indicate that the nanopatterned graphene approach can be a promising route for simultaneously tuning the optical and electrical properties of graphene to make it more light-transmissible and suitable as a flexible transparent conductor.

Nanopatterned Graphene Field Effect Transistor Fabricated Using Block Co-polymer Lithography

We demonstrate a successful fabrication of Nanopatterned Graphene (NPG) using a PS-b-P4VP polymer, which was never used previously for the graphene patterning. The NPG exhibits homogeneous mesh structures with an average neck width of ∼19 nm. Electronic characterization of single and few layers NPG FETs (field effect transistors) were performed at room temperature. We found that the sub-20 nm neck width creates a quantum confinement in NPG, which has led to a bandgap opening of ∼0.08 eV. This work also demonstrates that BCP (block co-polymer) lithography is a pathway for low-cost, high throughput large-scale production of NPG with critical dimensions down to the nanometer regime.

Fabrication of thin film TiO2 nanotube arrays on Co-28Cr-6Mo alloy by anodization.

Titanium oxide (TiO2) nanotube arrays were prepared by anodization of Ti/Au/Ti trilayer thin film DC sputtered onto forged and cast Co-28Cr-6Mo alloy substrate at 400 °C. Two different types of deposited film structures (Ti/Au/Ti trilayer and Ti monolayer), and two deposition temperatures (room temperature and 400 °C) were compared in this work. The concentrations of ammonium fluoride (NH4F) and H2O in glycerol electrolyte were varied to study their effect on the formation of TiO2 nanotube arrays on a forged and cast Co-28Cr-6Mo alloy. The results show that Ti/Au/Ti trilayer thin film and elevated temperature sputtered films are favorable for the formation of well-ordered nanotube arrays. The optimized electrolyte concentration for the growth of TiO2 nanotube arrays on forged and cast Co-28Cr-6Mo alloy was obtained. This work contains meaningful results for the application of a TiO2 nanotube coating to a CoCr alloy implant for potential next-generation orthopedic implant surface coatings with improved osseointegrative capabilities.

Fabrication and Magnetic Properties of Nonmagnetic Ion Implanted Magnetic Recording Films for Bit-Patterned Media

We have investigated the magnetic M-H loop characteristics of CoCrPt-SiO2 perpendicular recording media as influenced by nonmagnetic ion implantations. We have also developed patterned media via ion implantation using a convenient polymer nanomask approach for local control of coercivity of magnetically hard [Co/Pd]n multilayer film with a [Co 0.3 nm \Pd 0.8 nm] 8/Pd 3 nm/Ta 3 nm layer structure. The CoCrPt-SiO2 magnetic layer having perpendicular magnetic anisotropy is sputter deposited on a flat substrate. The [Co/Pd] n multilayer film with vertical magnetic anisotropy is deposited and the regions corresponding to the magnetic recording bit islands are coated with polymer islands using a nanoimprinting technique. Subsequent ion implantation allows patterned penetration of implanted ions into the [Co/Pd]n multilayer film, thus creating magnetically isolated bit island geometry while maintaining the overall flat geometry of the patterned media.