Preparation and characterization of the amorphous tungsten cone field emitter arrays by Ar etching

Uniform amorphous tungsten cone arrays in high density were fabricated by Ar⁺ reduction etching of WO₃ nanowire film. The etching process was performed in the analysis chamber of an X-ray photoelectron spectroscopy (XPS) system. SEM and TEM results revealed that the tip radius of the etched cones was 10 nm, and the cones were amorphous with a high aspect ratio of over 250. XPS analysis proved the cones to be metallic tungsten. In the aspect of field-emission property, the tungsten cone arrays had a lower turn-on field of 3 MV m⁻¹ compared with 5 MV m⁻¹ of the as-grown original WO₃ nanowire film.     

Structural and mechanical characteristics of (1 0 3) AlN thin films prepared by radio frequency magnetron sputtering

The (1 0 3)-oriented aluminum nitride (AlN) thin film is an attractive piezoelectric material for the applications in surface acoustic wave and film bulk acoustic wave resonator devices. In this work, we repot structural and mechanical characteristics of (1 0 3) AlN thin films deposited onto (1 0 0) Si substrates with radio frequency magnetron sputtering at different sputtering powers at 150, 250, and 350 W. Comparisons were made on their crystalline structures with X-ray diffraction, surface morphologies with atomic force microscopy, mechanical properties with nanoindentation, and tribological responses with nanoscratch. Results indicate that for the sputtering power of 350 W, a high-quality (1 0 3) AlN thin film, whose hardness is 18.91 ± 1.03 GPa and Young's modulus is 242.26 ± 8.92 GPa, was obtained with the most compact surface condition.     

Electro-tunable one-dimensional photonic crystal structures based on grooved silicon infiltrated with liquid crystal

The paper reports on composite periodic structures fabricated by means of wet anisotropic etching of (1 1 0)-oriented Si on a SOI platform and infiltrated with liquid crystal E7. The electro-optical effect under low voltages was registered for inter-digital structures by both optical microscopy and micro-Raman spectroscopy.     

Photon mapping of MgO thin films with an STM

The light emission from an STM junction consisting of an MgO thin film on Mo(0 0 1) and an Au tip is analyzed with respect to its spatial distribution for various excitation conditions. The spectral characteristic of the light is compatible with an emission mechanism mediated by tip-induced plasmons that are excited by inelastic electron tunneling involving field-emission resonances in the tip-sample gap. The dependence of field-emission resonances on the MgO work function allows the controlled stimulation of differently thick oxide islands in the photon maps by changing the sample bias.     

Effect of sputtered films on morphology of vertical aligned ZnO nanowires

Vertical aligned ZnO nanowires were grown by MOCVD technique on silicon substrate using ZnO and AlN thin films as seed layers. The shape of nanostructures was greatly influenced by the under laying surface. Vertical nanopencils were observed on ZnO/Si, whereas the nanowires on both sapphire and AlN/Si substrate have the similar aspect ratio. XRD patterns suggest that the nanostructures have good crystallinity. High-resolution transmission electron microscopy (HRTEM) confirmed the single crystalline growth of the ZnO nanowires along [0 0 1] direction. Room-temperature photoluminescence (PL) spectra of ZnO nanowires on AlN/Si clearly show a band-edge luminescence accompanied with a visible emission. More interestingly, no visible emission for the nanopencils on ZnO/Si substrates, were observed.     

Nonpolar a-plane GaN grown on r-plane sapphire using multilayer AlN buffer by metalorganic chemical vapor deposition

Mirror-like and pit-free non-polar a-plane (1 1 −2 0) GaN films are grown on r-plane (1 −1 0 2) sapphire substrates using metalorganic chemical vapor deposition (MOCVD) with multilayer high-low-high temperature AlN buffer layers. The buffer layer structure and film quality are essential to the growth of a flat, crack-free and pit-free a-plane GaN film. The multilayer AlN buffer structure includes a thin low-temperature-deposited AlN (LT-AlN) layer inserted into the high-temperature-deposited AlN (HT-AlN) layer. The results demonstrate that the multilayer AlN buffer structure can improve the surface morphology of the upper a-plane GaN film. The grown multilayer AlN buffer structure reduced the tensile stress on the AlN buffer layers and increased the compressive stress on the a-plane GaN film. The multilayer AlN buffer structure markedly improves the surface morphology of the a-plane GaN film, as revealed by scanning electron microscopy. The effects of various growth V/III ratios was investigated to obtain a-plane GaN films with better surface morphology. The mean roughness of the surface was 1.02 nm, as revealed by atomic force microscopy. Accordingly, the multilayer AlN buffer structure improves the surface morphology and facilitates the complete coalescence of the a-plane GaN layer.     

ZnO thin film deposition on butterfly shaped electrodes for ultraviolet sensing applications

ZnO thin film was deposited on patterned gold electrodes using sol–gel spin coating technique. Conventional photo-lithography with wet etching process was used to create butterfly shaped 13 μm gap from zero gap chrome mask. The deposited thin film was characterized structurally, morphologically and electrically using X-ray diffraction, scanning electron microscope and Kiethly sourcemeter. Current–voltage (I–V) characterization was captured in dark and UV conditions. The current gain of the fabricated device was 1.36 and the response and recovery time of the sensor was 76 s and 104 s, respectively, showed the fabricated device can be used for UV applications.     

Fabrication of <1 1 0> oriented tungsten nano-tips by field-assisted water etching

We report the field-assisted H₂O etching that enabled us to fabricate nano-tips from polycrystalline <1 1 0> oriented tungsten wires at room temperature. We optimized the sharpening procedure in order to obtain field emissions (FEs) with high collimation. The typical tip apex was composed of a large base and a nano-protrusion with a radius of curvature less than 3.5 Å. The narrowest opening angle (full width at half maximum) of the FE was 4.3° at 150 pA. We prepared two types of tips using two different applied bias voltages during the H₂O etching. The electron microscope images and the analysis of Fowler-Nordheim (FN) plots revealed that the sizes of the individual bases depended on the fixed bias voltages during the H₂O etching and affected their FE properties. In addition, we could confirm that the FE current from the nano-tip was more stable than that of the normal tip.     

Formation of high aspect ratio polyamide-6 nanofibers via electrically induced double layer during electrospinning

In the present study, the formation of high aspect ratio nanofibers in polyamide-6 was investigated as a function of applied voltage ranging from 15 to 25 kV using electrospinning technique. All other experimental parameters were kept constant. The electrospun polyamide-6 nanofibers were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF). FE-SEM images of polyamide-6 nanofibers showed that the diameter of the electrospun fiber was decreased with increasing applied voltage. At the critical applied voltage, the polymer solution was completely ionized to form the dense high aspect ratio nanofibers in between the main nanofibers. The diameter of the polyamide-6 nanofibers was observed to be in the range of 75-110 nm, whereas the high aspect ratio structures consisted of regularly distributed very fine nanofibers with diameters of about 9-28 nm. Trends in fiber diameter and diameter distribution were discussed for the high aspect ratio nanofibers. TEM results revealed that the formation of double layers in polyamide-6 nanofibers and then split-up into ultrafine fibers. The electrically induced double layer in combination with the polyelectrolytic nature of solution is proposed as the suitable mechanisms for the formation of high aspect ratio nanofibers in polyamide-6.     

Optical and electrical properties of different oriented CVD diamond films

Due to different oriented diamond films having different properties, in this paper optical and electrical properties of different oriented diamond films have been investigated. The measured results indicate diamond films are of high quality and the properties of the (0 0 1)-oriented diamond film are better than those of the (1 1 1)-oriented one. Refractive index and extinction coefficient of (0 0 1)-oriented diamond film in the wavelength range of 2.5-12.5 μm is 2.391 and in the order of 10⁻⁵, respectively. And for the (1 1 1)-oriented one it is 2.375 and in the order of 10⁻⁴. The dark current of the (0 0 1)-oriented diamond film is 33.7 nA under an applied electric field of 100 kV/cm. The resistivity of the (0 0 1)-oriented diamond film obtained is about 2.33 × 10¹⁰ Ω cm. The current of (0 0 1)-oriented diamond film is almost no change with the time testing.     

Antireflective structure imprinted on the surface of optical glass by SiC mold

An antireflective structure with two-dimensional 300-nm periodicity was fabricated on a phosphate glass surface using an imprinting process with a SiC mold. The optimized structure designed using RCWA calculation was a convex circular cone sharing the ridge line of adjacent cones. The SiC mold was fabricated using electron beam drawing and subsequent reactive ion etching with CHF₃ and O₂ gases. The glass’ surface reflectance was estimated as 0.2% at 530 nm wavelength, which was approximately 1/20 that of the optically polished surface.     

Correlation between local hysteresis and crystallite orientation in PZT thin films deposited on Si and MgO substrates

(0 0 1)-Oriented tetragonal ferroelectric PbZr_0.53Ti_0.47O₃ (PZT) thin films (90 nm of thickness) have been grown on TiO_x/Pt/TiO₂/SiO₂/Si and TiO_x/Pt/MgO substrates. The existence of (1 0 0)-oriented crystallites in the c-axis matrix of the (0 0 1)-oriented films has been evidenced by using four circles X-ray diffraction. Depending on the substrate, the ratio of the lattice parameters c/a was found to be 1.02 (Si) and 1.07 (MgO) and this was correlated with the coercive field values. Local piezoelectric hysteresis loops produced by atomic force microscopy have been taken with profit to characterize the switching properties of the ferroelectric domains at the scale of individual crystallites. In each case, (1 0 0)-oriented crystallites require much higher voltage than (0 0 1)-oriented crystallites for switching. These results are explained by taking into account the strain imposed by the substrate in the film. We conclude that piezoelectric hysteresis loops produced by atomic force microscopy provide very rich information for addressing the local switching property of individual crystallites in PZT thin films.     

Electron-assisted chemical etching of oxidized chromium

Electron-assisted chemical etching of oxidized chromium, CrO_x, has been studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). Two model substrates were used—10 nm CrO_x deposited on Si(1 0 0) that was covered with either native oxide or a 20 nm Au/Pd alloy film. Using chlorine and/or oxygen as etching gases, the experiments were conducted in a customized high vacuum system, equipped with a high density electron source and a low pressure reaction cell. On both substrates, electron-assisted chemical etching of CiO_x was detected by SEM, EDS and AFM. Making the method questionable for etching applications, there is substantial substrate damage associated with the etching. The SEM images indicate strongly inhomogeneous material removal, apparently initiated and propagated from specific but unidentified sites. In the experiments involving the Au/Pd film, there was phase separation of Au and Pd, and dewetting to form metallic islands. AFM data show that the etched holes were as deep as 200 nm, confirming relatively rapid etching of the Si substrate after the top layer of Cr oxide was removed.     

Reactive ion etching of FePt using inductively coupled plasma

We propose a reactive ion etching (RIE) process of an L1₀-FePt film which is expected as one of the promising materials for the perpendicular magnetic recording media. The etching was carried out using an inductively coupled plasma (ICP) RIE system and an etching gas combination of CH₄/O₂/NH₃ was employed. The L1₀-FePt films were deposited on (1 0 0)-oriented MgO substrates using a magnetron sputtering system. The etching masks of Ti were patterned on the FePt films lithographically. The etch rates of ∼16 and ∼0 nm/min were obtained for the FePt film and the Ti mask, respectively. The atomic force microscopy (AFM) analyses provided the average roughness (R_a) value of 0.95 nm for the etched FePt surface, that is, a very flat etched surface was obtained. Those results show that the highly selective RIE process of L1₀-FePt was successfully realized in the present study.     

Annealing effect on microstructure and mechanical properties of amorphous Al-C-N films

Al-C-N thin films with different Al contents were deposited on Si (1 0 0) substrates by closed-field unbalanced reactive magnetron sputtering in the mixture of argon and nitrogen gases. These films were subsequently vacuum-annealed at 700 °C and 1000 °C, respectively. The microstructures of as-deposited and annealed films were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM); while the hardness and elastic modulus values were measured by nano-indention method. The results indicated that the microstructure of both as-deposited and annealed Al-C-N films strongly depended on Al content. For thin films at low Al content, film delamination rather than crystallization occurred after the sample was annealed at 1000 °C. For thin films at high Al content, annealing led to the formation of AlN nanocrystallites, which produced nanocomposites of AlN embedded into amorphous matrices. Both the density and size of AlN nanocrystallites were found to decrease with increasing depth from the film surface. With increasing of annealing temperature, both hardness and elastic modulus values were decreased; this trend was decreased at high Al content. Annealing did not change elastic recovery property of Al-C-N thin films.     

Structure, dielectric and ferroelectric properties of highly (1 0 0)-oriented BaTiO3 grown under low-temperature conditions

The highly (1 0 0)-oriented BaTiO₃ thin films were fabricated on LaNiO₃(1 0 0)/Pt/Ti/SiO₂/Si substrates under low-temperature conditions. Substrate temperatures throughout the fabrication process remained at or below 400 °C, which allows this process to be compatible with many materials commonly used in integrated circuit manufacturing. X-ray diffraction data provided the evidence for single BaTiO₃ phase. Field-emission scanning electron microscopy was used to study the columnar structure of the films. The dielectric properties as a function of frequency in the range of 1 kHz to 1 MHz was obtained. The room temperature remanent polarization (2P_r) and coercive field were found to be ∼5 μC/cm² and 50 kV/cm, respectively. The BTO film maintains an excellent fatigue-free character even after 10⁹ switching cycles.     

Synthesis and characterization of (h 0 h)-oriented silicalite-1 films on α-Al2O3 substrates

A simple and well-designed synthesis procedure is proposed to fabricate silicalite-1 films on porous α-Al₂O₃ substrates on purpose of preventing the aluminum leaching. The continuous and 2 μm thick seed layer of silicalite-1 crystals is fabricated by using a spin coater. The first-time seeded growth is performed to synthesize a thin layer of intergrown ZSM-5 crystals on the silicalite-1 seed layer, where the use of low alkalinity and short synthesis time is to reduce the aluminum leaching. The intergrown layer of ZSM-5 crystals serves as a barrier to block the aluminum leaching from porous α-Al₂O₃ substrates in the second-time seeded growth, leading to the formation of ca. 11 μm thick intergrown and oriented silicalite-1 films with an extremely high Si/Al ratio. According to SEM images and XRD measurements, the as-synthesized silicalite-1 film is dense, continuous, and (1 0 1)-oriented. The electron probe microanalysis (EPMA) of the resulting film demonstrates that there is no aluminum leaching in the second-time seeded growth. The leaking tests confirm that non-zeolitic pores in the silicalite-1 film are negligible.     

Effect of Cr and V dopants on the chemical stability of AZO thin film

The effect of the dopants of Cr and V on the optoelectronic properties of AZO thin film by pulsed DC magnetron sputtering has been investigated. We also use HCl and KOH solutions to conduct the chemical stability of AZO:Cr:V thin film. The experimental results show that the optimum AZO optoelectronic properties without Cr and V doping obtain the resistivity of 9.87 × 10⁻⁴ Ω cm, optical transmittance of 84% and surface roughness rms value of 2.6 nm. The chemical stability of AZO will increase after Cr and V doping. Under the added V = 0.19 wt.%, Cr = 0.56 wt.%, AZO:Cr:V thin film showed 52% increased chemical stability and 128% decrease in surface roughness after etching (the resistivity was 3.62 × 10⁻³ Ω cm and optical transmittance 81%). From the experimental results, the higher resistivity obtained after KOH etching compared with after HCl etching. The reason is that the Zn/Al ratio will reduce after etching and cause the AZO film carrier density to reduce as well. However, the optical transmittance obtained after KOH etching will be higher than that after HCl etching. This is because that a better surface roughness after KOH etching obtained than after HCl etching.     

Optimization on technical parameters for fabrication of SDC film by screen-printing used as electrolyte in IT-SOFC

Sm-doped Ceria (SDC) electrolyte film was successfully fabricated on anode substrate of NiO-SDC by screen-printing. Some technical parameters for fabrication were investigated and optimized, including printing times, ink composition and sintering temperature. Scanning electron microscope (SEM) measurement was done to check the microstructures of SDC film and single cell. The parameters greatly affected the quality of SDC film and cell performance. The single cell with the optimum parameters exhibited an OCV of 0.82 V and a power density of 0.5 W/cm² at 600 °C.     

Characterization of heat-assisted magnetic probe recording on CoNi/Pt multilayers

A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2–7 V were applied to a CoNi/Pt multilayered film fabricated on either bare silicon or oxidized silicon substrates. Different types of Ir/Pt and W STM tips were used in the experiment. The results show that thermally recorded magnetic marks are formed with a nearly uniform mark size of 170 nm on the film fabricated on bare silicon substrate when the pulse voltage is above a threshold voltage. The mark size becomes 260 nm when they are written on the identical film fabricated on an oxidized silicon substrate. The threshold voltage depends on the material work function of the tip, with W having a threshold voltage about 1 V lower than Pt. A synthesized model, which contains the calculation of the emission current, the simulation of heat transfer during heating, and the study of magnetic domain formation, was introduced to explain experimental results. The simulation agrees well with the experiments.