Ion Polishing Research Articles

Method of formation of super-smooth optical surfaces using GCIB and ANAB processing

Optical glass–ceramic is a promising material for the elements of precision optical systems operating in a wide temperature range. However, conventional methods such as the chemical–mechanical or ion polishing do not allow to form a substrate surface with less than 0.2 nm root mean square roughness. The method of gas cluster ion beam (GCIB) and accelerated neutral atom beam (ANAB) processing of glass–ceramic substrates is proposed to obtain super-smooth optical surfaces.The experimental samples were characterized by atomic force microscopy and X-ray diffractometry. It is shown that the surface is modified with the disappearance of linear defects (scratches) and the roughness parameters are improved. Only residual chaotic relief with the average roughness value (Ra) of 0.2 – 0.3 nm is observed after GCIB treatment. Subsequent ANAB processing allows to decrease the Ra parameter down to 0.15 nm. The improvement of surface characteristics is confirmed by the analysis of PSD-function in the investigated range of spatial frequencies. As a result of this work the method for super-smooth optical substrates fabrication was developed and the characteristics of obtained surfaces were investigated.

On the formation of temperature-induced defects at the surface of TEM specimens prepared from TiAl using high-energy Gallium and low-energy Argon ions

ABSTRACT Specimens for transmission electron microscopic (TEM) investigations were prepared from γ titanium aluminide alloys with Gallium and Argon ions using a focused ion beam (FIB) and a precision ion polishing system (PIPS). Preparation to electron transparency by Gallium ions alone leads to the formation of crystalline platelets of the α titanium phase at the specimen surfaces, revealed through conventional and high resolution (HR) TEM analysis. The platelets are assumed to precipitate from priorly formed amorphous layers. The required crystallisation temperature of about 480°C is generated through the ion bombardment implying that the γ titanium aluminides can be heated substantively during sputtering. The primary reason for this is the restricted transfer of heat away from the beam impact point when the specimen thickness comes close to the beam diameter. The formation of the platelets can be avoided by terminating the Gallium ion treatment prior to that, while providing for a sufficient thermal bonding of the specimen to the grid as well and polishing off the remaining material by Argon ions, which are much less focused and less energetic, so that the local heat peaks are reduced.

Features of large-scale thin foils fabrication for transmission electron microscopy by focused ion beam

Focused ion beam (FIB) sample preparation for transmission electron microscopy is a well established technique. However there are some problems related with high-quality large-scale (over 10 um) sample preparation of thin foils. In this work we demonstrate the successful preparation of such samples on example of ferrite steel sample and present the refined lift-out preparation technique, which was applied here. All sample preparation has been carried out in conventional single-beam FIB Hitachi FB-2100 with additional low-kV Ar+ ion polishing.

W/B short period multilayer structures for soft x-rays

X-ray W/B multilayer mirrors with a period of 2.5 nm were deposited by dc magnetron sputtering and studied in comparison with W/Si multilayer systems of the same period. Transmission electron microscopy, grazing incidence X-Ray reflectivity, and x-ray photoelectron spectroscopy analysis revealed that the layer quality and interfaces of the W/B multilayers are not better than those of the W/Si multilayers. Strong intermixing between W and B is present, which leads to compound formation with little or no pure W left after the interaction: an optically unfavorable boride formation and an increased roughness result in a reduced reflectivity. The deposited W/B multilayer mirrors showed a reflectivity of 34.5% at 0.84 nm and angle of incidence 9.7°, compared to 40% obtained for W/Si multilayers. Ion polishing applied on the boron layers did not result in improvements of the reflectivity.

Highly Strained Au Nanoparticles for Improved Electrocatalysis of Ethanol Oxidation Reaction.

Au is an ideal noble metal for use as an electrocatalyst for the ethanol oxidation reaction owing to its high performance-to-cost ratio. The catalyst usually exists as nanoparticles (NPs) for high surface area-to-volume ratio. In the present work, a nontraditional physical approach has been developed to fabricate ultrasmall and homogeneous single-crystalline Au NPs by ion bombardment in a precision ion polishing system. Transmission electron microscopy characterizations show that the Au NPs produced with 5 keV Ar+ are highly strained to form twinned crystals, which accumulate a large amount of surface energy, and this was found to be an underlying reason causing strong catalysis. Electrochemistry tests reveal that in alkaline medium the C1 pathway occurs much more preferentially with the strained Au NPs than the normal Au NPs. The surface area-to-volume ratio is no longer the only factor that affects the performance; instead, surface energy might play a more important role in enhancing the catalytic activities.

Application of SEM and EDS for mineral composition of shale gas reservoir

In recent years, great progress has been made in the exploration and exploitation of shale gas, making it the main driving force for the growth of world natural gas production. Mineral composition restricts the pore size, distribution, geometry and connectivity of shale reservoirs, and also affects the brittleness and fracturing ability of shale reservoirs. Therefore, mineral composition is of great significance to the evaluation and exploration and development of shale gas reservoirs. Taking the Paleogene shale reservoir in Liaozhong Sag as an example, this study explored the application of argon ion polishing technology, Field Emission Scanning Electron Microscope (FE-SEM) and X-ray Energy Dispersive Spectrometer (EDS) analysis in mineral identification.

The characteristics of nano-pore of the 3rd member shale from Dongying Formation of Paleogene in Liaozhong Sag

The reservoirs structure and pore characteristics of shale have greatly influenced the reservoir, adsorption and migration of oil and gas, and have become one of the important contents of reservoir physical characteristics evaluation. The organic-rich shales in the 3rd member shale of the Dongying Formation in Paleogene, Liaozhong sag, Bohai bay basin were studied in this paper. Firstly, the surface of shale sample was etched by argon ion polishing technology, and then the microscopic pore morphology was observed by field emission environment scanning electron microscope. The results show that: 1) the pores of shale reservoir in 3rd member shale of the Dongying Formation from Liaozhong sag are divided into inorganic pores (including intergranular pores, intragranular pores, interstratal pores and intercrystalline pores), organic pores and microfractures; 2) the intergranular pores are largely developed, intragranular pores and interlaminar pores are relatively developed, micro-cracks are less developed, and intergranular pores and organic pores are rarely developed.

Effect of Oxide Composition on the Orientation Relationship and Disregistry in Complex Nucleus of Ti and Nb Stabilized Ferritic Stainless Steel Revealed by EBSD Measurement

The compositions and crystal orientations of complex nuclei in an industrial Ti and Nb stabilized ferritic stainless steel (FSS) with a high equiaxed zone ratio were investigated to evaluate the nucleation efficiency of (Ti,Nb)(CN) on the surface of oxides. Although the thermodynamic analysis showed that the equilibrium oxide is Ti2O3, two other types of oxides mainly composed of MgAl2O4 were found in the complex nucleus. In addition, the oxide with the lowest melting temperature was found to have the smallest size. The crystal orientation relationships among MgAl2O4, Ti2O3 and (Ti,Nb)(CN) were revealed by the application of micro-area EBSD measurement after argon ion polishing (AIP) treatment. The crystal planes and crystal orientations of the MgAl2O4 are found to be completely parallel to (Ti,Nb)(CN). In the complex nucleus dominated by Ti2O3, it was found that {001}Ti2O3 is parallel to {111}(Ti,Nb)(CN) and {100}Ti2O3 is parallel to {110}(Ti,Nb)(CN). According to these orientation relationships, Ti2O3 was calculated to have a much lower disregistry with (Ti,Nb)(CN) than MgAl2O4. In addition, it was also revealed by orientation relationships that (Ti,Nb)(CN) has great potential for the nucleation of δ-Fe.

Microstructure and Electrochemistry of Al-Rich Primer

The Al-rich primer, developed by NAVAIR is designed to be anodic relative to high strength Al alloys such as AA2XXX and AA7XXX, so that it drives the mixed potential of the Al alloy substrates into a cathodic region below the breakdown potentials of Al alloys, preventing localized corrosion. The Al-rich primer under study is composed of spherical Al-Zn-In pigments and epoxy binder. The spherical pigments are achieved from atomization of Al-Zn-In bulk sacrificial anode used on hulls of boats operating in seawater. The size of spherical pigments in the primer ranges from with size ranging from a few hundreds of nanometers to tens of microns. The average size of the pigments is around 7 µm in diameter. The active Al-Zn-In pigments are further treated with trivalent chromium passivation (TCP) solution for different dwell times to reduce the self-corrosion of the pigments. In this study, the Al-rich primer coated on TCP-treated AA2024-T3 substrate provided by NAVAIR was investigated. The microstructure of the Al-rich primer was studied using a combination of X-ray microscopy (XRM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. 3D reconstruction microstructure of the Al-rich primer was acquired by XRM, showing that the primer contains Al-Zn-In particles with various sizes, epoxy and a significant volume of voids. The planar and cross-section views of the Al-rich primer were also examined by SEM. Since mechanical polishing damaged the pigments and smeared epoxy, so ion polishing was used to prepare the planar and cross-sectional samples of the Al-rich primer to reduce materials damage and achieve a less-damaged surface. Similar to what was found in XRM results, voids were also found in the primer. In addition, some relatively large Al-Zn-In pigments with size of tens of microns were surrounded by some very fine Al-Zn-In pigments with size of a few hundred of nanometers to form agglomerates. The cross-section view examined by TEM showed that some fine pigments directly contacted large pigments, and others bonded with epoxy. Heavy elements enriched at grain boundaries in the pigments. STEM-EDS mapping will be conducted on the pigments. To understand the electrochemistry of Al-Zn-In pigments, the microstructure and electrochemistry of Al-Zn-In bulk alloy were studied. Zn enriched along grain boundaries in bulk alloy. Large intermetallic particles with size of tens of microns located at grain boundaries. Some intermetallic particles were enriched with Fe and Si, and some were enriched with In. In situoptical microscopy was used to observe the pitting initiation and growth on the both polished and TCP-treated Al-Zn-In bulk alloy during anodic potentiodynamic polarization in 3.5% NaCl solution. Pits initiated around some intermetallic particles. The composition of these particles will be determined. When the primer is exposed to bulk solution or salt spray environment, electrolyte saturates the epoxy. Thus, the environment in which the substrate and Al-Zn-In pigments are surrounded is not bulk solution or electrolyte layer on the primer surface, but electrolyte saturated in epoxy. To simulate the environment of the primer, the special coplanar electrodes were designed. Ag/AgCl electrode was used as reference electrode; pure Ni was chosen as counter electrode; working electrode was AA2024 or Al-Zn-In bulk alloy. Three electrodes were mounted in epoxy and then polished. The neat primer without pigments were applied on the polished surface of coplanar electrodes. The coplanar electrodes were immersed in 3.5 wt% NaCl solution. The neat primer was saturated with electrolyte after 24 h of immersion. Potentiodynamic polarization and electrochemical impedance spectroscopy tests were conducted to measure the electrochemistry under the neat primer. Galvanic corrosion between the AA2024 substrate and Al-Zn-In bulk alloy was also studied. Each alloy was connected with electrical wires, and then both of them were put side by side with around 2 mm separation and then mounted in epoxy. The galvanic panels were polished and then exposed to NaCl solution or salt spray chamber. Galvanic currents between them were measured during exposure. The experiments are ongoing.

Ethanol Gas Sensors Based on ZnO Nanotube Structures Fabricated By Atomic Layer Deposition

Among various Metal Oxide Semiconductor (MOS) gas sensors, ZnO nanostructure gas sensors have been widely used due to its large exciton binding energy, wide band gape of 3.37 eV, large exciton binding energy of 60 meV at room temperature, good electrical conductivity, low cost, and high mechanical stability. Furthermore, a variety of morphology has been developed to improve the properties and applications. In this work, ZnO nanotube nanostructures were fabricated as gas sensors to sense ethanol vapor due to its high electrochemical stability, nontoxicity, and, especially, high surface-to-volume ratio. Several coaxial ZnO nanotubes were synthesized on porous substrate to further enhance the sensing response to ethanol vapor with increased reaction surfaces in ZnO nanostructures. In this study, ZnO nanotubes were synthesized by Atomic Layer Deposition (ALD) on Anodic Aluminum Oxide (AAO) templates with sacrificial Al2O3 layers. The second Al2O3 sacrificial layer followed by ZnO layer was synthesized on AAO samples by ALD with TMA (Al2(CH3)6) and DI water as precursors. In addition, the third ZnO thin film layer were deposited on the surface of the sacrificial layer of Al2O3 with precisely controlled thickness by ALD. The entire procedure outlined above for fabricating ZnO-Al2O3-ZnO structures is considered as one super cycle. More super cycles were applied to synthesize additional coaxial ZnO nanotubes. To eliminate the sacrificial layer, a Precision Ion Polishing System (PIPS) was used to remove the top cover as shown in Figure 1. Therefore, the Al2O3 sacrificial layers were exposed for Sodium Hydroxide (NaOH) wet etching. After the sacrificial layers were removed by NaOH, ZnO nanotube gas sensors were formed as shown in Figure 1 (b). To investigate the sensing performance of ZnO nanotube gas sensors to ethanol vapors, a gas sensor testing system was developed with a sealed reaction chamber and a control system with stable temperature control and accurate gas concentration control. The sensing performance of the MOS gas sensors consisting of only core single crystal ZnO nanotubes, was compared to sensors consisting of double nested coaxial ZnO nanotubes, and further compared to three nested tube-in-tube coaxial ZnO nanotube structures and analyzed under various ethanol vapor concentrations at different temperatures. The ZnO nanostructures sensing results on ethanol vapor demonstrated the sensing performance was considerably enhanced due to the increased surface to volume ratio in the ZnO tube structures. Figure 1

Low-energy ion polishing of Si in W/Si soft X-ray multilayer structures

The effect of ion polishing in sputter deposited W/Si multilayer mirrors with a d-spacing of 2.5 nm was studied. 0.1 to 0.5 nm of Si were etched with 100 eV Ar+ ions. This process resulted in a pronounced reduction in diffused scattering, measured at wavelengths about 0.1 nm. However, CuKa X-ray specular reflectivity and AFM showed only a marginal reduction of the roughness amplitude in the systems. Furthermore, the soft X-ray reflectivity at 0.84 and 2.4 nm did not show any changes after the ion polishing as compared to the nonpolished structures. Grazing incidence X-ray reflectivity (GIXR) analysis revealed that there was no pure W present in the deposited multilayers, with WSi2 being formed instead. As a result, it was concluded that the initial roughness in W/Si multilayers grown by magnetron sputtering is not the major factor in the reflectivity deviation from the calculated value for an ideal system. Nevertheless, the grazing incidence small-angle X-ray scattering (GISAXS) analysis revealed that ion polishing reduces the vertical propagation of roughness from layer to layer by a factor of two, as well as favorably affecting the lateral correlation length and Hurst parameter. These improvements explain the reduction of diffused X-ray scattering at 0.1 nm by more than an order of magnitude, which is relevant for applications like high resolution XRD analysis.

Pore characteristics and evolution of Wufeng–Longmaxi Fms shale gas reservoirs in the basin-margin transition zone of SE Chongqing

At present, researches on the pore evolution of shale reservoir and its evolution mechanism are still at such a groping stage that a consensus has not yet reached. Based on core analysis and thermal simulation experiments, the pore types, pore structures and pore-size change rules of shale gas reservoirs of Upper Ordovician Wufeng–Lower Silurian Longmaxi Fms in the southeastern (SE) Sichuan Basin and its basin-margin transition zone (hereinafter referred to as the basin-margin transition zone of SE Chongqing) were studied by means of argon ion polishing–scanning electron microscopy (SEM) and atomic force microscopy. Then, the evolution characteristics of organic pores were discussed, and the influence of associated minerals on pore evolution was analyzed. Finally, a pore evolution model for the shale gas reservoirs in this area was established. And the following research results were obtained. First, three types of reservoir spaces are mainly developed in the high-quality shale reservoirs of Wufeng–Longmaxi Fms in this area, including fracture, inorganic pore and organic pore. And the organic pores provide the primary reservoir space of shale gas, which can be divided into four categories, i.e., amorphous kerogen pores, structured kerogen pores, asphaltene pores and paleontology fossil pores. Second, organic contracted fractures are related to the contraction of organic matters, first appearing on one side of the organic matters and then becomes wider and wider with the increase of temperatures. Third, organic pores are mostly the “spongy” pores distributed densely inside the organic matters. When Ro is in the range of 1.56–3.50%, macropores and mesopores are dominant. And when Ro exceeds 3.50%, macropores decrease while mesopores and micropores increase. Fourth, the types of organic matters and the content of associated minerals (e.g. clay minerals, siliceous particles and pyrite) play an important role in the development of pores. In conclusion, the pore evolution law of Wufeng–Longmaxi shale in the basin-margin transition zone of SE Chongqing is that with the increase of burial depth, inorganic porosity decreases significantly, organic porosity increases first and then decreases, and the total porosity shows a change trend of decreasing first, then increasing and finally decreasing continuously.

The Controlling Effects of Compositions on Nanopore Structure of Over-Mature Shale from the Longtan Formation in the Laochang Area, Eastern Yunnan, China

Over-mature shale has undergone complex geological processes, e.g., diagenesis, deep thermolysis, epigenesis, and metamorphism. During this series of processes, the internal components of shale are transformed coordinatively, and the special pore structure with a complex genesis in the over-mature shale is formed. The study of the special pore structure of over-mature shale and its main controlling factors can provide theoretical support for shale gas exploration and development. In this study, the over-mature shale of the Longtan Formation in the Laochang area, eastern Yunnan Province, China, was tested and analyzed to determine the total organic carbon content, kerogen microscopic composition, and its vitrinite reflectance. Moreover, the mineral composition and pore characteristics of the shale were tested using X-ray diffraction, the argon ion polishing field emission scanning electron microscopy technique, and the low temperature nitrogen adsorption experiment. The results show that the compositions of Longtan Formation shales have a low rigid clastic particles content, high clay content, and abundant metasomatic ankerite, and that the organic matter, dominated by type III, is highly mature. At the same time, the shale pore structure is characterized by a large average pore size, well-developed macropores, and a high number of micropores and mesopores. By analyzing the transformation of the mineral composition of shale during thermal evolution, the controlling factors of pore structure are determined. During the evolution of shale, the intergranular pores (mainly large pores) between rigid minerals are destroyed in large quantities. After a short period, a large number of dissolved pores with the pore size of macropores are formed in the acid-resistant minerals under the action of organic acid. These dissolved pores, together with the remaining intergranular pores of rigid minerals and micro-fractures, form most of the macropores of shale. There is a large amount of ankerite in over-mature shale formed during metasomatism, which occludes some pores of shale. However, intragranular pores and cleavage-sheets develop in ankerite, contributing some porosity to the shale reservoir. Inter-clay pores and organic matter pores constitute most shale micro and mesopores, and between which inter-clay pores take dominance.

Ultrasmooth beryllium substrates for solar astronomy in extreme ultraviolet wavelengths.

The paper describes a multistage method of forming ultrasmooth substrates based on bulk beryllium. Such substrates are suggested to be used for multilayer extreme ultraviolet mirrors of spacecraft missions on solar corona investigations in the spectral range 17.1-58.4nm. The technique for chemical nickel plating of the sample surface is described. The process parameters that provide the formation of an amorphous film with a thickness of about 100 microns are presented. The results of mechanical polishing are shown. The effective roughness of 1.3nm is obtained, which is twice lower than one achievable for a nickel-free beryllium surface. The applicability of the ion beam figuring technique is demonstrated: the initial surface roughness of a nickel film after etching with Ar ions (Eion=200-800 eV) to a depth of 250nm does not deteriorate. The amorphous silicon film deposition followed by ion polishing made it possible to reduce the microroughness (atomic force microscope frame 2×2 μm) to σ2×2=0.15 nm from the initial σ2×2=0.46 nm. The reflectivity of multilayer mirrors deposited on these substrates turned out to be close to the values obtained on "witnesses" (supersmooth silicon substrates). Moreover, for the Mg/MoSi2 mirror optimized for the wavelength λ=58.4 nm the values of the reflection coefficients of structures on the beryllium substrate and on the silicon "witness" were identical (about 28%).

Large current ion beam polishing and characterization of mechanically finished titanium alloy (Ti6Al4V) surface

Ti6Al4V samples with a surface roughness of about 0.2 μm were polished by a high fluence ion beam source, and influences of the ion current, energy and incident angle on the surface roughness of Ti6Al4V were studied. The as-polished surfaces were characterized by laser scanning confocal microscopy (LSCM), atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS). The LSCM images revealed that the density of pits in the original surface decreased greatly after the ion polishing process. In addition, the surface roughness calculated from these images proved that the mean value reduced to 53 nm with an ion energy, current and incident angle of 600 eV, 130 mA and 75°, respectively. The smoothing effect was also confirmed by the power spectral density (PSD) functions calculated from the AFM data. GIXRD patterns indicated that the Ti6Al4V samples mainly contain the hexagonal close packed (HCP) α-Ti, no recognizable peaks corresponding to the body centered cubic (BCC) β-Ti were observed. Furthermore, after the ion beam polishing process, the phase of all the as-polished samples kept steady. The XPS results revealed that C, O, Ti, Al and V were present in both the original as well as the polished samples. In addition, due to the highly reactive characteristics of Ti, Al and V elements, a higher signal for oxygen can also be observed on the outermost surface of the ion beam polished samples. The polishing process of Ti6Al4V surface bombarded by Ar ion beam is also simulated by binary collision approximation (BCA) code SDTrimSP, the effects of ion beam energy and incident angle on the sputtering yield were investigated. The results showed that the sputtering yield of Ti, Al and V atoms increased almost linearly with the ion energy. However, as for the influence of ion incident angle, the sputtering yield first increased gradually from 0° and peaked at about 65°, then decreased rapidly because the incident angle is too large for Ar ion to penetrate into the surface of Ti6Al4V sample.

Quantitative evaluation of organic porosity and inorganic porosity in shale gas reservoirs using logging data

ABSTRACTReservoir pores space characterization is the core content of shale gas reservoir evaluation. The reservoir pore space of shale gas reservoir is complex, which can be divided into organic pore, clay pore, crack pore, and debris pore. A method for evaluating the four porosity of shale gas reservoir by using logging data is presented in this paper. First, according to the volume model, shale rock is equivalent to three parts: matrix, organic matter, and pore. On this basis, response equations of density logging and neutron logging are constructed. The total porosity of shale reservoirs can be solved by combining the two equations. Second, organic pore is nanopore that remains in organic matter during the conversion of kerogen to oil and gas, which is related to the content and maturity of organic matter. An equation for calculating organic porosity using total organic carbon content and density logging is presented. The scale factor in the equation is obtained from argon ion polishing scanning electron microscope experimental data. Third, based on the GRI porosity experimental data of 8 samples in the study area, the relationship among clay porosity, clay bound water saturation, and clay content was analyzed. It is considered that the clay bound water saturation has a certain correlation with the clay content, but the correlation coefficient is not high, has a positive correlation with the clay content. Based on this, a statistical model of clay porosity, clay content, and total porosity was established. Fourth, based on the dual laterolog response characteristics of microcracks, the fracture porosity of shale reservoirs is calculated by positive and negative simulation proposed by Li et al. In addition, the detrital porosity is equal to the difference between total porosity and organic porosity, clay porosity, crack porosity. The above techniques are applied to the calculation of four porosities of two wells in the Longmaxi Formation of Sichuan basin, China, and good effect has been achieved.

Features of Ion-Beam Polishing of the Surface of Sapphire

The effect of an argon ion beam on the surface of sapphire is studied at different technological parameters: the ion energy, and the angle α between the sapphire surface and the ion-beam axis. The roughness of the sapphire surface is analyzed before and after ion polishing. The optimum ion-beam parameters are determined, at which the surface roughness after polishing decreases to 0.8 nm. At angles α = 20°–30°, the relief of the sapphire surface is found to become wavy. The study of the impact of the ion energy on the roughness of the sapphire surface in the 400–1200-eV range reveals that an increase in the energy of the ion beam to 1200 eV is accompanied with a decrease by 8.8 times in the roughness which falls below the level of 3 nm.

Polishing the surface of a z-cut KDP crystal by neutralized argon ions.

The sputtering yield and dynamics of the surface roughness of the potassium dihydrogenphosphate-KH2PO4 (KDP) crystal z-cut was initially polished by precision micromilling with a diamond cutter, after which surface treatment by neutralized Ar ions was studied. The sputtering yield turned out to be noticeably higher than the values for materials that are amenable to ion polishing (fused silica, ULE, Zerodur, etc.), but the polishing effect at angles of incidence of 0°, 30°, and 45° was found. A record value of the effective surface roughness in the spatial frequencies range of ν∈[4.9·10-2-6.3·101 μm-1]σeff=0.61 nm was obtained.

Sensing Enhancement on ZnO Nanorod Gas Sensors with Novel Nanorod/Nanotube Structures

Among various Metal Oxide Semiconductor (MOS) materials for in gas sensor applications, ZnO has been widely used in gas detection due to its wide band gape of 3.37 eV, large exciton binding energy (~60 meV), good electrical conductivity, and high mechanical stability. Moreover, owning to the high surface-to-volume ratio, ZnO gas sensors based on nanorod structure are extensively applied into gas specie detection and gas concentration detection. Therefore, a large number of methods and techniques have been applied to enhance the sensing performance of ZnO nanorod gas sensors. In this work, the ZnO nanorods with coaxial nanotubes gas sensors were fabricated to detect the concentration of ethanol vapor under the different temperatures and concentration conditions. In addition, Al doped ZnO (AZO) thin films were deposited on the surface of ZnO nanorods by Atomic Layer Deposition (ALD). The additional oxygen vacancies deficiency from the Zn-O and Al-O bands in the Zn-Al-O interface could improve the sensing performance of prepared ZnO gas sensors. In this study, ZnO nanorods were synthesized by hydrothermal method with ZnO seed layers deposited on Si wafer by ALD, as shown in Figure 1(a). The solutions used for ZnO nanorods hydrothermal growth were prepared with zinc nitrate hexahydrate (Zn(NO3)6H2O) and hexamethylenetetramine ((CH2)6N4) dissolved in DI water. To synthesize ZnO nanotubes around nanorods, one additional Al2O3 sacrificial layer was deposited on the surface of ZnO nanorods by ALD with TMA (Al2(CH3)6) and DI water as precursors. Then ZnO thin films were deposited on ZnO nanorods with Al2O3 sacrificial layer wrapped around, as shown in Figure 1(b). To eliminate the sacrificial layer, Precision Ion Polishing System (PIPS) was used to remove the top cover of ZnO nanorods. Figure 1(c) and Figure 1(d) show the Al2O3 sacrificial layer was exposed for Sodium hydroxide (NaOH) etching. After the sacrificial layer was removed by NaOH, ZnO nanorod/nanotube gas sensors were synthesized, as shown in Figure 1(e). To further enhance the sensing performance of ZnO nanorod/nanotube to the ethanol, AZO thin films were deposited on the surface by ALD as shown in Figure 1(f). A testing system of gas sensors was developed with a sealed reaction chamber and control system based on CompactRio from National instrument to investigate the sensing performance of ZnO nanorod/nanotube to ethanol vapor. The sensing response of ZnO nanorods to ethanol vapor was recorded and analyzed from the resistance change of ZnO nanorods. The sensing performances of ZnO nanorods, ZnO nanorod/nanotube, and ZnO nanorod/nanotube after coated with AZO thin films were measured and analyzed under various volumes of ethanol vapor at different temperatures. Base on the results, the sensing performance of ZnO nanorod gas sensor was enhanced by increase surface-to-volume ratio and oxygen vacancies. Figure 1. FESEM results of (a) ZnO Nanorods, (b) ZnO Nanorods with Al2O3 Coating and ZnO thin films, (c) and (d) Al2O3 sacrificial layer exposed after PIPS, (e) ZnO Nanorod/Nanotube after NaOH Etching, (f) ZnO Nanorod/Nanotube with AZO Coating. Figure 1

Atomic Force Microscopy Studies of Severely Deformed Amorphous TiNiCu Alloy

The amorphous Ti50Ni25Cu25 alloy was subjected to high pressure torsion (HPT) processing. TEM studies revealed in the structure of the HPT-processed samples the presence of nanocrystals with a size of about 5 nm and amorphous clusters with a size of about 10-30 nm. Atomic force microscopy (AFM) was used to study the surface morphology of foils prepared by ion polishing from the initial amorphous ribbons and HPT-processed samples. AFM images of the foil prepared from the initial ribbon revealed a smooth surface with an average roughness of 0.3 nm. A totally different surface morphology was observed for the foil prepared from the HPT-processed state by the same regime of ion polishing: the presence of holes with a depth of 2-4 nm and a width of 10-30 nm. The changes in the surface morphology, namely the holes-like surface morphology of the HPT-processed state, could be explained by a complex transformation of the amorphous structure, and probably by the variation and redistribution of free volume, which leads to the emergence of a cluster contrast in TEM images.