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This paper describes the science underlying the synthesis and characterization of microcrystalline diamond (MCD) to ultrananocrystalline diamond (UNCD) films on hafnium oxide (HfO2) thin films, grown on flat Si substrates and micro-pillars on Si substrates, for the first time. HfO2 is used as a novel inter-phase layer for the integration of microcrystalline (1–3 μm grain size), nanocrystalline (10–200 nm grain size), and ultrananocrystalline diamond (3–5 nm grain size) as coatings on substrates used in transformational technologies such as silicon, oxides, and metals that need protective corrosion/mechanical abrasion resistant coatings developed in this work. Atomic layer deposition was used to grow HfO2 films with 5, 10, 30 and 100 nm in thickness, while hot filament chemical vapor deposition was used to grow diamond films, respectively. High resolution transmission electron microscopy, X-ray photoelectron and Raman spectroscopies revealed the formation of an atomic scale hafnium carbide (HfC) interphase layer on the surface of the HfO2 film, which provides efficient nucleation for diamond film growth to produce tailored diamond surfaces on flat Si substrates and Si micro-pillars on flat Si substrates, for new transformational micro/nano-electronics and other high-tech technologies.

This paper focuses on reporting systematic studies on the effect of the precursor gas chemistry ratio between hydrogen/methane (H2/CH4) and argon (Ar) to tailor control of the grain size, morphology and roughness of large area diamond films. Films ranging from a microcrystalline diamond structure (MCD 1–3 μm grain size) all the way to an ultrananocrystalline diamond (UNCD 3–7 nm grain size) structure were grown over 100 mm diameter areas, as a pathway for scaling diamond film growth processes by Hot Filament Chemical Vapor Deposition (HFCVD) to large areas (≥ 150 mm in diameter). H2-rich/CH4 chemistry was used to synthesize the MCD films, while Ar-rich/CH4/H2 chemistry was used to grow the UNCD films. The synthesis of the diamond films using the HFCVD process indicates that the Ar content is critical to achieve the characteristic UNCD film structure with roughness, chemical bonding and thickness uniformity in the range of 5% across large areas. The ratio of Ar/H2 in the range 70/30 sccm to 90/10 sccm, all with 2 sccm of CH4 gas, yields films with grain size from 10–50 nm for nanocrystalline diamond (NCD) films to 3–7 nm for the UNCD films, respectively. The extremely smooth UNCD films (~ 3–5 nm rms) are achieved using Ar (90 sccm)/H2 (10 sccm)/CH4 (2 sccm) gas flows.

The confined porous environment of metal organic frameworks (MOFs) is an attractive system for studying reaction mechanisms. Compared to flat oxide surfaces, MOFs have the key advantage that they exhibit a well-defined structure and present significantly fewer challenges in experimental characterization. As an example of an important reaction, we study here the dissociation of water—which plays a critical role in biology, chemistry, and materials science—in MOFs and show how the knowledge of the structure in this confined environment allows for an unprecedented level of understanding and control. In particular, combining in-situ infrared spectroscopy and first-principles calculations, we show that the water dissociation reaction can be selectively controlled inside Zn-MOF-74 by alcohol, through both chemical and physical interactions. Methanol is observed to speed up water dissociation by 25% to 100%, depending on the alcohol partial pressure. On the other hand, co-adsorption of isopropanol reduces the speed of the water reaction, due mostly to steric interactions. In addition, we also investigate the stability of the product state after the water dissociation has occurred and find that the presence of additional water significantly stabilizes the dissociated state. Our results show that precise control of reactions within nano-porous materials is possible, opening the way for advances in fields ranging from catalysis to electrochemistry and sensors.

The effect of a polycrystalline silicon (poly-Si) seeding layer on the properties of relaxor Pb(Zr0.53,Ti0.47)O3–Pb(Zn1/3,Nb2/3)O3 (PZT–PZN) thin films and energy-harvesting cantilevers was studied. We deposited thin films of the relaxor on two substrates, with and without a poly-Si seeding layer. The seeding layer, which also served as a sacrificial layer to facilitate cantilever release, was found to improve morphology, phase purity, crystal orientation, and electrical properties. We attributed these results to reduction of the number of nucleation sites and, therefore, to an increase in relaxor film grain size. The areal power density of the wet-based released harvester was measured. The power density output of the energy harvester with this relaxor composition and the poly-Si seeding layer was 325 μW/cm2.

© 2016 American Chemical Society. We have designed and synthesized an isoreticular series of luminescent metal-organic frameworks (LMOFs) by incorporating a strongly emissive molecular fluorophore and functionally diverse colinkers into Zn-based structures. The three-dimensional porous networks of LMOF-261, -262, and -263 represent a unique/new type of nets, classified as a 2-nodal, (4,4)-c net (mot-e type) with 4-fold, class IIIa interpenetration. All compounds crystallize in a body-centered tetragonal crystal system (space group I41/a). A systematic study has been implemented to analyze their interactions with heavy metals. LMOF-263 exhibits impressive water stability, high porosity, and strong luminescence, making it an excellent candidate as a fluorescent chemical sensor and adsorbent for aqueous contaminants. It is extremely responsive to toxic heavy metals at a parts per billion level (3.3 ppb Hg2+, 19.7 ppb Pb2+) and demonstrates high selectivity for heavy metals over light metals, with detection ratios of 167.4 and 209.5 for Hg2+/Ca2+and Hg2+/Mg2+, respectively. Mixed-metal adsorption experiments also show that LMOF-263 selectively adsorbs Hg2+over other heavy metal ions in addition to light metals. The Pb2+KSVvalue for LMOF-263 (55,017 M-1) is the highest among LMOFs reported to date, and the Hg2+KSVvalue is the second highest (459,446 M-1). LMOF-263 exhibits a maximum adsorption capacity of 380 mg Hg2+/g. The Hg2+adsorption process follows pseudo-second-order kinetics, removing 99.1% of the metal within 30 min. An in situ XPS study provides insight to help understand the interaction mechanism between Hg2+and LMOF-263. No other MOFs have demonstrated such a high performance in both the detection and the capture of Hg2+from aqueous solution.

Using infrared spectroscopy combined with ab initio methods we study reactions of H$_2$O and CO inside the confined spaces of Zn-MOF-74 channels. Our results show that, once the water dissociation reaction H$_2$O$\;\rightarrow\;$OH+H takes place at the metal centers, the addition of 40 Torr of CO at 200 $^{\circ}$C starts the production of formic acid via OH+H+CO$\;\rightarrow\;$HCO$_2$H. Our detailed analysis shows that the overall reaction H$_2$O+CO$\;\rightarrow\;$HCO$_2$H takes place in the confinement of MOF-74 without an external catalyst, unlike the same reaction on flat surfaces. This discovery has several important consequences: It opens the door to a new set of catalytic reactions inside the channels of the MOF-74 system, it suggests that a recovery of the MOF's adsorption capacity is possible after it has been exposed to water (which in turn stabilizes its crystal structure), and it produces the important industrial feedstock formic acid.

We show that the water dissociation reaction H$_2$O$\rightarrow$OH+H in the confined environment of MOF-74 channels can be precisely controlled by the addition of the noble gas He. Elucidating the entire reaction process with ab initio methods and infrared (IR) spectroscopy, we prove that the interaction between water molecules is critical to the formation of water clusters, which reduce the dissociation barrier by up to 37% and thus influence the reaction significantly. Our time-resolved IR measurements confirm that the formation of these clusters can be suppressed by introducing He gas, providing unprecedented control over water dissociation rates. Since the water dissociation reaction is the cause of the structural instability of MOF-74 in the presence of water, our finding of the reaction mechanism lays the groundwork for designing water stable versions of MOF-74 as well as understanding water related phenomena in MOFs in general.

Metal organic framework (MOF) materials in general, and MOF-74 in particular, have promising properties for many technologically important processes. However, their instability under humid conditions severely restricts practical use. We show that this instability and the accompanying reduction of the CO$_2$ uptake capacity of MOF-74 under humid conditions originate in the water dissociation reaction H$_2$O$\rightarrow$OH+H at the metal centers. After this dissociation, the OH groups coordinate to the metal centers, explaining the reduction in the MOF's CO$_2$ uptake capacity. This reduction thus strongly depends on the catalytic activity of MOF-74 towards the water dissociation reaction. We further show that-while the water molecules themselves only have a negligible effect on the crystal structure of MOF-74-the OH and H products of the dissociation reaction significantly weaken the MOF framework and lead to the observed crystal structure breakdown. With this knowledge, we propose a way to suppress this particular reaction by modifying the MOF-74 structure to increase the water dissociation energy barrier and thus control the stability of the system under humid conditions.

Lead zirconate titanate, Pb(Zr 0.53 ,Ti 0.47 )O 3 or PZT, thin films and integrated cantilevers have been fabricated for energy harvesting applications. The PZT films were deposited on PECVD SiO 2 /Si substrates with a sol–gel derived ZrO 2 buffer layer. It is found that lead content in the starting solution and ramp rate during film crystallization are critical to achieving large-grained films on the ZrO 2 surface. The electrical properties of the PZT films were measured using metal–ferroelectric–metal and inter-digital electrode structures, and revealed substantial improvement in film properties by controlling the process conditions. Functional cantilevers are demonstrated using the optimized films with output of 1.4 V peak-to-peak at 1 kHz and 2.5 g.

0.9Pb(Zr0.53,Ti0.47)O3-0.1Pb(Zn1/3,Nb2/3)O3 (PZT–PZN) thin films and integrated cantilevers have been fabricated. The PZT–PZN films were deposited on SiO2/Si or SiO2/Si3N4/SiO2/poly-Si/Si membranes capped with a sol–gel-derived ZrO2 buffer layer. It is found that the membrane layer stack, lead content, existence of a template layer of PbTiO3 (PT), and ramp rate during film crystallization are critical for obtaining large-grained, single-phase PZT–PZN films on the ZrO2 surface. By controlling these parameters, the electrical properties of the PZT–PZN films, their microstructure, and phase purity were significantly improved. PZT–PZN films with a dielectric constant of 700 to 920 were obtained, depending on the underlying stack structure.

In the present study a complete analysis of the morphological and electrical properties of PZT layers with composition 53Zr-47Ti is presented. Three different samples composed of 3, 6, and 9 PZT layers were analyzed on a substrate consisting of ZrO2-SiO2-Si structures. The PZT and ZrO2 layers were deposited via Sol-Gel, whereas the SiO2 layer, on every sample, was deposited via PECVD. SEM results showed morphology of very small granules on the 3 layered thin-film samples (12 nm), on the 6 layered thin-film samples a mixture of small and large size (100-300 nm) granule formation was observed, with the 9 layered thin-film samples exhibiting very large granule sizes (bigger than 300 nm). XRD results showed that increasing the number of deposited layers caused an incremental increase on the detected peak intensities, aided in the promotion of the perovskite phase, and diminished the presence of the pyrochlore phase. It was also observed, during electrical measurements, that increasing the number deposited layers directly increased the overall capacitance of the thin-film structure. This effect was attributed primarily to the large amount of perovskite and large size of grains presented on thick samples.

A complete analysis of the morphology, crystallographic orientation, and resulting electrical properties of Pb(Zr0.53,Ti0.47) Pb(Nb1/3, Zn2/3)O3 (PZT-PZN) thin films, as well as the electrical behavior when integrated in a cantilever for energy harvesting applications, is presented. The PZT-PZN films were deposited using sol-gel methods. We report that using 20% excess Pb, a nucleation layer of PbTiO3 (PT), and a fast ramp rate provides large grains, as well as denser films. The PZT-PZN is deposited on a stack of TiO2/PECVD SiO2/Si3N4/thermal SiO2/Poly-Si/Si. This stack is designed to allow wet-etching the poly-Si layer to release the cantilever structures. It was also found that the introduction of the poly-Si layer results in larger grains in the PZT-PZN film. PZT-PZN films with a dielectric constant of 3200 and maximum polarization of 30 μC/cm2 were obtained. The fabricated cantilever devices produced ~300–400 mV peak-to-peak depending on the cantilever design. Experimental results are compared with simulations.

In this research, BiFeO3 (BFO) films are integrated into BFO/SrTiO3 (STO)/BFO nanolaminates (BSB-NLs) featuring nanometer-scale thickness of BFO and STO layers. By introducing the STO layer in between two BFO layers, the leakage current density is reduced by two orders of magnitude with respect to relatively high leakage currents of current single BFO layers, i.e., from 10−5 A/cm2 to 10−7 A/cm2. The BSB-NL also shows very high piezoelectric response, which is ∼5 times higher than that of the pure BFO with the same thickness. The highly strained state of the BFO layers concurrently with the chemical/crystallographic state of the interfaces between the BFO and STO layers contribute to the very high values of piezoresponse and very low leakage current observed in the BSB-NLs.