Whether the presence of adsorbates increases or decreases thermal conductivity in metalorganic frameworks (MOFs) has been an open question. Here we report observations of thermal transport in the metal-organic framework HKUST-1 in the presence of various liquid adsorbates: water, methanol, and ethanol. Experimental thermoreflectance measurements were performed on single crystals and thin films, and theoretical predictions were made using molecular dynamics simulations. We find that the thermal conductivity of HKUST-1 decreases by 40-80% depending on the adsorbate, a result that cannot be explained by effective medium approximations. Our findings demonstrate that adsorbates introduce additional phonon scattering in HKUST-1, which particularly shortens the lifetimes of lowfrequency phonon modes. As a result, the system thermal conductivity is lowered to a greater extent than the increase expected by the creation of additional heat transfer channels. Finally, we show that thermal diffusivity is even more greatly reduced than thermal conductivity by adsorption.
SURMOF (surface-anchored metal-organic frameworks) thin films exhibit exciting chemical and physical properties, which can be modulated in as traightforward fashion to achieve specific benefits for numerousa pplications in future technologies. Here, we report ad etailed characterizationo fr esistive switching in crystalline SURMOF films of around % 10, % 20 and % 50 nm thicknesses. These demonstrated switching characteristics combined with the ability to deposit monolithically oriented crystalline HKUST-1 films with well-definedt hicknesses in the nm-range on conductive substrates serving as bottom electrodes and to lithographically fabricatet op-electrodes opens up the possibility to employ these metal-organich ybrid materials as solid state devices for potential nonvolatile resistive random access memory (RRAM)m emory applications. MOF bipolar switchingR RAM devices based on SURMOFs with thicknesses of 10 AE 5nm, 20 AE 5nma nd 50 AE 5nms how exceptionally promising performance. The huge flexibility of MOF materials with regards to devicea pplications is demonstrated by loading guest molecules into the pores of these framework materials. In the case of ferrocene infiltration,w es how that the already impressive performance of the SURMOF-RRAM devicesc an be furtheri mproved. The resultsd emonstrate the great potential of SURMOF thin films for the implementation of novel and scalable active materials for the next generation of digitalp rocessing and organic-based microelectronic devices.
The challenges of reducing gate leakage current and dielectric breakdown beyond the 45 nm technology node have shifted engineers' attention from the traditional and proven dielectric SiO 2 to materials of higher dielectric constant also known as high-k materials such as hafnium oxide ͑HfO 2 ͒ and aluminum oxide ͑Al 2 O 3 ͒. These high-k materials are projected to replace silicon oxide ͑SiO 2 ͒. In order to address the complex process integration and reliability issues, it is important to investigate the mechanical properties of these dielectric materials in addition to their electrical properties. In this study, HfO 2 and Al 2 O 3 have been fabricated using atomic layer deposition ͑ALD͒ on ͑100͒ p-type Si wafers. Using nanoindentation and the continuous stiffness method, we report the elastomechanical properties of HfO 2 and Al 2 O 3 on Si. ALD HfO 2 thin films were measured to have a hardness of 9.5 Ϯ 2 GPa and a modulus of 220 Ϯ 40 GPa, whereas the ALD Al 2 O 3 thin films have a hardness of 10.5 Ϯ 2 GPa and a modulus of 220 Ϯ 40 GPa. The two materials are also distinguished by very different interface properties. HfO 2 forms a hafnium silicate interlayer, which influences its nanoindentation properties close to the interface with the Si substrate, while Al 2 O 3 does not exhibit any interlayer.For the past 40 years the microelectronics industry has relied on the scaling down of device size in order to improve the performance, functionality, and bit density of chips, as described by Moore's law. As microelectronics is transitioning into deep nanotechnology, the drawback of the increasing miniaturization of devices is the increase of gate leakage current and oxide breakdown. 1 To reduce the gate leakage current and breakdown field across the gate insulator, researchers are looking into high-k dielectric materials. High-k materials such as HfO 2 and Al 2 O 3 will increase the transistor drive current and the transistor switching speed. 2 HfO 2 is predicted to replace SiO 2 , SiO x N y , and Si 3 N 4 as the gate dielectric of complementary metal oxide semiconductor ͑CMOS͒ devices at the 45 nm technology node and beyond. HfO 2 and Al 2 O 3 have dielectric constants of approximately k = 25 and 8, respectively, 3 which compare favorably with k = 3.9 for SiO 2 . Various deposition techniques have been used to deposit high-k materials. Among these growth techniques are metallorganic chemical vapor deposition ͑MOCVD͒, 4-6 pulsed laser deposition ͑PLD͒, 7 and atomic layer deposition ͑ALD͒. 4-6,8 MOCVD and PLD require a high temperature during processing and film fabrication. 9 For example, a minimum temperature of 600°C is required to deposit HfO 2 with MOCVD, whereas HfO 2 crystallizes once the temperature reaches 600°C. 10 ALD is a chemical reactionbased deposition technique that requires only relatively low temperatures. ALD provides absolute film deposition uniformity ͑atomic layer by atomic layer͒, precise composition control, high conformality, and completely self-limiting surface reactions, which makes ALD the most...
Nested multiple-walled coaxial nanotube structures of transition metal oxides, semiconductors, and metals were successfully synthesized by atomic layer deposition (ALD) techniques utilizing nanoporous anodic aluminum oxide (AAO) as templates. In order to fabricate free-standing tube-in-tube nanostructures, successive ALD nanotubes were grown on the interior template walls of the AAO nanochannels. The coaxial nanotubes were alternated by sacrificial spacers of ALD Al(2)O(3), to be chemically removed to release the nanotubes from the AAO template. In this study, we synthesized a novel nanostructure with up to five nested coaxial nanotubes within AAO templates. This synthesis can be extended to fabricate n-times tube-in-tube nanostructures of different materials with applications in multisensors, broadband detectors, nanocapacitors, and photovoltaic cells.
Whenever a nanoindent is placed near an edge, such as the free edge of the specimen or heterophase interface intersecting the surface, the elastic discontinuity associated with the edge produces artifacts in the load–depth data. Unless properly handled in the data analysis, the artifacts can produce spurious results that obscure any real trends in properties as functions of position. Previously, we showed that the artifacts can be understood in terms of a structural compliance, Cs, which is independent of the size of the indent. In the present work, the utility of the SYS (Stone, Yoder, Sproul) correlation is demonstrated in its ability to remove the artifacts caused by Cs. We investigate properties: (i) near the surface of an extruded polymethyl methacrylate rod tested in cross section, (ii) of compound corner middle lamellae of loblolly pine (Pinus taeda) surrounded by relatively stiff wood cell walls, (iii) of wood cell walls embedded in a polypropylene matrix with some poorly bonded wood–matrix interfaces, (iv) of AlB2 particles embedded in an aluminum matrix, and (v) of silicon-on-insulator thin film on substrate near the free edge of the specimen.
Lithographically defined microporous templates in conjunction with the atomic layer deposition (ALD) technique enable remarkable control of complex novel nested nanotube structures. So far three-dimensional control of physical process parameters has not been fully realized with high precision resolution, and requires optimization in order to achieve a wider range of potential applications. Furthermore, the combination of composite insulating oxide layers alternating with semiconducting layers and metals can provide various types of novel applications and eventually provide unique and advanced levels of multifunctional nanoscale devices. Semiconducting TiO 2 nanotubes have potential applications in photovoltaic devices. The combination of nanostructured semiconducting materials with nested metal nanotubes has the potential to produce novel multifunctional vertically-ordered three-dimensional nanodevices. Platinum growth by ALD has been explored, covering the initial stages of the thin film nucleation process and the synthesis of high aspect ratio nanotube structures. The penetration depth of the Pt into porous templates having various pore sizes and aspect ratios has been investigated. Several multi-walled nested TiO 2 -Pt nanotubes in series have been successfully fabricated using microporous Si templates. These innovative nested nanostructures have the potential to produce novel multifunctional vertically-ordered three-dimensional nanodevices in photovoltaic and sensing technologies. KEYWORDSAtomic layer deposition (ALD) platinum nanotubes, semiconductor/metal nanotubes, microporous Si templates, nanoporous alumina templates, multilayer nested nanotubes For several decades, the fabrication of nanostructures having highly-ordered, complex architectures has been one of the most interesting research topics. These structures have the potential to advance current technologies and enable the development of newer and more innovative applications of all kinds. In the past few years, vertically-ordered, self-organized nanotubes and nanorods have been synthesized using anodic aluminum oxide (AAO) or silicon (Si) nano/micropore templates. Most coaxial nanotubes currently produced with nanotemplates maintain three-dimensional scales close to those of the original Nano
Molecular-dynamics simulations and in situ experimental observations of the melting and equilibrium structure of the crystalline Si(100)-melt interface are described. The equilibrium interface is structured, exhibiting facets established on (111)planes. PACS numbers: 68.55.Rt, 64.70.Dv, 68.45.KgThe study of the solid-vapor and solid-liquid interfaces has attracted a recent surge of interest because of improved experimental and theoretical techniques for probing phenomena such as surface melting, surface roughening, and interface morphology. In particular,
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