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Piezoelectric materials convert external mechanical force into electrical energy, due to the breaking of the centrosymmetry of the atomic structure. Piezoelectricity-based nano-generators (PNGs) based on two-dimensional transition metal dichalcogenides (TMDs) can generate electrical energy stably by the piezoelectric effect at their nanoscale thickness. However, the commercialization of TMD-based PNGs is limited by their poor piezoelectric performance and microscale energy harvesting. Here, we present the first centimeter-scale PNGs based on molybdenum disulfide (MoS2) nanosheets with vertically grown hollow MoS2 nanoflakes (v-MoS2 NFs) obtained by chemical vapor deposition for energy harvesting from human motions. The collision of v-MoS2 NFs with a preferred odd-atomic-layer number and their 2H antiparallel phase leads to efficient electrical energy generation during the bending movement. Further, basal MoS2 films with v-MoS2 NFs are transferred onto flexible substrates via conventional polymer-assisted methods for the fabrication of attachable and wearable piezoelectric power generators.

Well-aligned crystalline carbon nanotubes (CNTs) were synthesized on anodic aluminum oxide (AAO) template using low-pressure thermal chemical vapor deposition (TCVD). The AAO templates were fabricated using an anodization process, and Fe as a catalyst was electrochemically deposited inside the bottom of the pores on the AAO template. For promotion of catalytic reaction of Fe, pore widening and catalyst reduction were performed. The enhancement of the catalytic reaction between C2H2 and the Fe catalyst particles results in CNTs with good crystallinity and a high packing density without the deposition of amorphous carbon on the pore surface of the AAO templates. The diameter and density of the CNTs were approximately 50 nm and 7×109 CNTs/cm2 (70% of pore density), respectively. When the threshold voltage of the electron emission was measured with a gap of 300 µm, it showed a very low turn-on field of 0.87 V/µm and the field enhancement factor was greater than 5600.

We have investigated the role of N2 in the synthesis of carbon nanotubes (CNTs) by dc hot-filament plasma-enhanced chemical vapor deposition. An NH3 and C2H2 gas mixture with a ratio of 4:1 was used as a precursor for the synthesis of CNTs on nickel-coated TiN/Si (100) substrates. N2 gas was introduced at a flow rate of 30–120 sccm with the precursor. The structure and composition of CNTs synthesized with/without N2 were investigated by scanning electron microscopy, transmission electron microscopy, X-ray photoemission spectroscopy (XPS), and Raman spectroscopy. The multiwalled carbon nanotubes (MWCNTs) synthesized with N2 were 2–5 times longer than those synthesized without N2, and the morphology of the MWCNTs was improved. An XPS core level spectrum shows that nitrogen is in the CNX and C–NH2 forms.

We have investigated the 6H-SiC(0001) √3×√3 R30° and 3×3 surfaces using the valence band spectra and the workfunction change as a function of the Na coverage. The Na-induced ionization energy shift of the √3×√3 R30° surface at the minimum value of the workfunction is in good agreement with the calculated one based on the Si-T4 model in which Na is adsorbed at all DBs. Similar workfunction changes suggest that the 6H-SiC(0001) 3×3 surface has the same density of reactive sites (1/3 ML) as the √3×√3 R30° surface. This result is interpreted in the framework of current models of the 3×3 reconstruction. In particular, we show that the results are not compatible with the accepted Erlangen-Jena model.

The direct synthesis of carbon nanotubes (CNTs) on substrates by chemical vapor deposition (CVD) is a highly promising route for their application to field emission displays. Several stringent requirements have to be met for this purpose, including low-temperature growth below 600°C to utilize glass substrates and large-area deposition for practical use. In this study, we carried out the synthesis of CNTs by thermal CVD on glass substrates at temperatures as low as 500–550°C. CNTs were grown by thermal decomposition of CO and H2 gases at atmospheric pressure for different thicknesses of Invar (Fe–Ni–Co alloy) catalytic layers. The CNT growth was strongly correlated with the preparation conditions of the catalytic layers. The diameters and heights of as-grown CNTs increased with the catalytic layer thickness from 2 nm to 30 nm. Measurements of the field emission properties of the CNTs showed that the threshold electric fields decreased with increasing thickness of the catalytic layers. Uniform electron emission was observed over a large area of 150×150 mm2 with high emission current and high brightness.

Images of uniformly illuminated sensors for the Large Synoptic Survey Telescope have circular periodic patterns with an appearance similar to tree rings. These patterns are caused by circularly symmetric variations of the dopant concentration in the monocrystal silicon boule induced by the manufacturing process. Non-uniform charge density results in the parasitic electric field inside the silicon sensor, which may distort shapes of astronomical sources. In this study we analyzed data from fifteen LSST sensors produced by ITL to determine the main parameters of the tree rings: amplitude and period, and also variability across the sensors tested at Brookhaven National Laboratory. Tree ring pattern has a weak dependence on the wavelength. However the ring amplitude gets smaller as wavelength gets longer, since longer wavelengths penetrate deeper into the silicon. Tree ring amplitude gets larger as it gets closer to the outer part of the wafer, from 0.1 to 1.0%, indicating that the resistivity variation is larger for larger radii.

A facile method was developed for chemical vapor deposition (CVD) growth of large-scale vertically oriented molybdenum disulfide nanoflakes on a basal MoS2 thin film (v-MoS2 on MoS2-TF) utilizing a porphyrin-type organic promoter layer, which catalyzed the synthesis and allowed large scale growth of v-MoS2 on MoS2-TF. Here, the growing density of the vertical MoS2 flakes was manipulated by adjusting the growth temperature and the thickness of the organic promoter layers. The v-MoS2 on MoS2-TF is even transferrable to arbitrary flexible substrates using the wet-transfer method without inducing noticeable amount of defects. A thin-film transistor was fabricated to determine the electrical property of the v-MoS2 on MoS2-TF film. Significantly, the vertically grown MoS2 was also applicable as the catalyst for hydrogen evolution reaction, which demonstrated a decreased overpotential by 1/3 of those by horizontally grown MoS2 or other CVD-grown crystalline MoS2 thin films previously reported.

The Ag-adsorbed Si(110)2×16 surfaces were investigated using low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). When Ag was deposited on a Si(110)2×16 surface at room temperature (RT) and annealed at several elevated temperatures, diffuse 1×1, 1×2+streak, 1×2, and (-1, 6)×(-7, 0) structures were observed by LEED. The relative Ag coverage of the reconstructed structures were estimated from Ag(MNN)/Si(LVV) AES intensity ratios and previous results. The structural model of the Ag/Si(110)1×2 surface was proposed from the LEED and AES results.

In this paper, a novel Al2O3/ZnO/Al2O3 stack is proposed as the silicon passivation layer for c-Si solar cell application. Recently, the Al2O3 film has been proved to be effective for passivating the p-type c-Si surface by forming the negative fixed oxide charge. It is confirmed by this experiment that the amount of negative fixed oxide charge can be controlled by inserting a ZnO interlayer (IL), which is explained by acceptor-like defect (VZn, Oi, and OZn) formation determined by the room-temperature photoluminescence (RTPL) analysis. The effect of ZnO IL is investigated using Al2O3 bottom layers of various thicknesses by electrical and physical analyses. The effective lifetime measurement shows that the electronic recombination losses at the silicon surface are reduced effectively by optimizing the Al2O3/ZnO/Al2O3 stack.

Here, we demonstrate the decoration of Ni nanoparticles (NPs) on graphene films by simple annealing for p-type doping of graphene. Scanning electron microscopy and atomic force microscopy revealed that high-density, uniformly sized Ni NPs were formed on the graphene films. The density of the Ni NPs increased gradually, whereas the size of the Ni NPs decreased with increasing NiCl2·6H2O solution concentration. The formation of Ni NPs on graphene films was explained by heat-driven dechlorination and subsequent nano-particlization, as investigated by X-ray photoelectron spectroscopy. The doping effect of Ni NPs onto graphene films was verified by Raman spectroscopy and electrical transport measurements. This method may provide a facile and universal way to obtain metal NPs on graphene if the metal forms a compound with Cl.

Vertically aligned carbon nanotubes (CNTs) were synthesized inside an array of dome-structured amorphous silicon (a-Si) holes on glass substrates. An a-Si layer swelled up as amorphous carbon (a-C) was grown to penetrate beneath the a-Si layer through patterned holes during thermal chemical vapor deposition (CVD), leading to an array of a-Si domes filled with a-C. Following the etching of a-C inside the domes, vertically aligned CNTs were selectively grown inside an array of hollow dome-structured holes using alternating-current plasma-enhanced chemical vapor deposition. The potential of applying this structure to gated field emitter arrays was discussed.

Size-tailored Fe catalytic nanoparticles (NPs) were formed by a heat-driven evaporation process, and precise control of single-walled carbon nanotube (SWCNT) diameter was achieved. The size and surface concentration of Fe NPs significantly decreased with increasing evaporation temperature, which was investigated by transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy. TEM and Raman spectroscopy revealed that the synthesis of SWCNTs with an extremely narrow diameter distribution was achieved and their diameter can be manipulated by evaporation temperature. This diameter-controlled growth of SWCNTs is a step towards SWCNT-based applications.

In-situ X-ray photoemission spectroscopy (XPS) has been used to investigate the initial stages of TiO2 growth on a Si(001) substrate by atomic layer deposition (ALD). The core level spectra of Si 2p, C 1s, O 1s, and Ti 2p were measured at every half reaction in the titanium tetra-isopropoxide (TTIP)–H2O ALD process. The ligand exchange reactions were verified using the periodic oscillation of the C 1s concentration, as well as changes in the hydroxyl concentration. XPS analysis revealed that Ti2O3 and Si oxide were formed at the initial stages of TiO2 growth. A stoichiometric TiO2 layer was dominantly formed after two cycles and was chemically saturated after four cycles.

An optimum thickness of Al2O3 support layer (ASL) for growth of singlewalled carbon nanotubes (SWCNTs) was systematically established. Atomic force microscopy and scanning electron microscopy results clearly revealed that increasing ASL thickness (t ASL) resulted in increased ASL grain diameter and root mean square roughness. This significantly affected the diameters of CNTs through the restricted formation of Fe nanoparticles. As a result, SWCNTs and multiwalled CNTs were simultaneously synthesized using ASLs with t ASL = 5, 50, and 100 nm, which were confirmed using Raman spectroscopy and transmission electron microscopy. In contrast, ASLs with t ASL = 10–30 nm, were suitable for predominant growth of SWCNTs, and ASL with t ASL = 15 nm was especially effective for growing high-quality SWCNTs with a small diameter and narrow distribution, 1.1±0.15 nm.

Au and Pt nanoparticles (NPs) were anchored on multiwalled carbon nanotubes (MWCNTs) via electron beam induced amorphous carbon encapsulation by energy-tunable MeV electron beam irradiation (MEBI) under ambient conditions. MEBI allowed the formation of size-homogeneous Au and Pt NPs on MWCNTs, as observed by transmission electron microscopy. Anchoring of metal NPs was achieved by MEBI-induced amorphous carbon encapsulation. The chemical doping effects of Au and Pt NPs were also verified by Raman spectroscopy. MEBI may provide a facile methodology for anchoring metal NPs to enhance electrical conductivity without destruction of MWCNTs.

Millimeter-scale, vertically aligned carbon nanotubes (CNTs) were grown at a relatively low temperature of 700 °C by the microwave plasma chemical vapor deposition. Oxygen and water were used to investigate their role in the growth rate and crystallinity of CNTs. Scanning electron microscopy and transmission electron microscopy were adopted to observe the height and number of walls of the CNTs, respectively. The addition of oxygen significantly increased the growth rate of CNTs (∼23 µm/min) for 70 min, which is three and two times higher than that of normal CNTs and water-assisted CNTs, respectively. Furthermore, the high growth rate was maintained for 220 min and the crystallinity of CNTs, which was evaluated by the G to D band ratio in Raman spectra, was also greatly improved only by introducing oxygen.

We suggest a novel process for fabricating a carbon nanotube field emission source having one carbon nanotube per gate aperture. The fabrication is based on UV lithography, instead of electron beam lithography. We used only one patterning step to define the gate, insulator, and cathode. We applied a DC voltage to the anode and a pulse signal to the gate. We then investigated the I-V characteristics of the structure, changing the frequency and the duty-cycle of the pulse signal applied to the gate. We found that the optimum frequency and duty-cycle were 250 kHz and 22%, respectively. The structure had a turn-on voltage of 1.1 V under these conditions. The anode voltage did not have much effect. Finally, we checked the stability of the source for 40 h. We obtained an average emission current of 1.093 µA with a standard deviation of 1.019 × 10(-2) µA.

We have investigated the electronic structure of graphite oxide using X-ray absorption spectroscopy at the carbon and oxygen K-edges. The unoccupied π* and σ* states associated with sp2 hybridization in graphite, are also apparent in the graphite oxide, which indicates that it has a graphitic structure even though it experiences oxidation and annealing. Additional electronic states of the graphite oxide which are not present in its precursor, graphite, are ascribed to the functional groups such as epoxide, carboxyl, and hydroxyl groups.

An asymmetric electrostatic-quadrupole lens (AEQL) system for high definition field emission displays (HD-FEDs) was proposed. It was applied to the double-gated structure where the emitters are a thick layer of carbon nanotube paste such as a flat surface emitter. The AEQL structure was designed with two opposing planar electrodes of noncircular apertures which generate the quadrupole electric field. Utilizing a design of field emitter arrays (FEAs) with AEQL, an optimized beam shape with horizontal reduction and vertical elongation was obtained. According to three-dimensional (3D) simulation results, this AEQL structure exhibited excellent focusing effects that satisfied the aspects of pixel size and shape in HD-FEDs.

We have investigated the Sb-induced phase transition of the reconstructed Si(112) surface by low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). A sharp sixfold hexagonal LEED pattern was observed when Sb was deposited on the clean Si(112) surface at 300°C, corresponding to the bulk-terminated 1×1 structure of the Si(111) surface. From the LEED pattern and the XPS results, we suggest a surface structure corresponding to the LEED pattern with (111) - 1×1 + weak 5×1 spots for the Sb/Si(112) surface.

The growth mechanism of Si film on a CeO2(111)/Si(111) substrate has been investigated using X-ray diffraction (XRD), double crystal XRD (DCXRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). We have epitaxially grown a CeO2 film on the Si(111) surface by deposition of CeO2 at 640°C. When Si was deposited at 620°C on the CeO2(111)/Si(111) substrate using a high-vacuum e-beam evaporator, it was observed from XRD analysis that the Si film grew along the [111] direction. The TEM and AFM images showed that the top Si layer consists of large mountains and deep valleys. The XPS data showed no segregation of Ce on the Si layer surface. However, there was slight diffusion of Ce along the top layer Si grain boundary. These analysis results reveal that at the early stage of deposition, Si crystal nuclei are formed on a domain of the CeO2 film on Si(111) and grow three-dimensionally along the [111] direction, and eventually these merge into large mountains.

We investigated Sb-induced reconstruction on a Si(113)3×2 surface using low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). Depending on the annealing temperature and Sb coverage, 1×1, 1×2+2×, 2×2, and 2×5 structures were observed. The 2×2 and 2×5 structures showed reversible phase transitions to 1×2 and 1×5 structures respectively at high temperature. The relative Sb coverages of the 1×1 and 2×2 structures formed by annealing at about 400 and 700°C were measured from Sb 3d/Si 2p core-level XPS intensity ratios.

We have investigated Cs-induced reconstruction on the Si(113)3×2 surface using low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). For Cs deposition at room temperature, the (3×1) LEED pattern was observed for a wide Cs coverage range. At high substrate temperatures, the (3×1), (1×5+2×) and (2×2) phases were observed with increasing Cs deposition time. The relative Cs saturation coverages of (3×1)-Cs at RT and (2×2)-Cs at 300°C were measured from Cs 3d/Si 2p core level XPS intensity ratios. The results are summarized in a phase diagram as a function of the Cs deposition time.

Magnetization measurements were performed on Bi1.4Pb0.6Ca2Sr2Cu3O y superconductor with T c=108 K using a vibrating sample magnetometer in fields up to 18 kOe. The magnetization M(T) is linearly increased in a temperature range of about 15 K below T c, and the temperature dependence of H c2 is obtained from the onset of diamagnetism. From the upper critical field slope ∂H c2/∂T, the zero-temperature upper critical field H c2(0) is estimated about 61 T. Also, the lower critical field H c1(0) is 111 Oe using the magnetization measurement M(H). From the magnetic critical fields H c2 and H c1, we estimate the superconducting parameters: the coherence length ζ0=23 Å, the penetration depth λ0=2600 Å, the Ginzburg-Landau parameter κ=113 and the jump in the specific heat ΔC/T c≃2 mJ/molK2.

It is found by X-ray photoelectron spectroscopy and LEED that the saturation coverage of Bi is one monolayer for the Si(111)√3×√3-Bi surface. Azimuthal dependence of Bi 4d photoelectron diffraction has been measured for the Si(111)√3×√3-Bi surface and analyzed kinematically. The results of the analysis have confirmed the presence of Bi-triplets with sides of 3.1 Å as proposed by X-ray diffraction. It is further found that the Bi-triplets form an overlayer on the substrate.

We measured the electrical resistivity ρ(T) of the Bi2-xPbxCa2Sr2Cu3Oy(x=0.2, 0.4, 0.6) system withTc\cong108 K in air and in the temperature range of 20 KT2whereT2is in the range 610–680 K, depending upon the sample composition. The resistivity saturation was not observed over the temperature range we measured. From the linear behaviour of ρ(T), we estimated the order to magnitude of the electron-phonon coupling constant λ and the electron mean free pathlof high-Tcsuperconducting Bi-compounds in the high-temperature region.

Surface reconstructions of a submonolayer Sb/Si(111) system were investigated by low-energy electron diffraction and X-ray photoelectron spectroscopy. It has been found that the surface superstructures of diffuse 2×2 (or three-domain 2×1), √3×√3, 5√3×5√3 and 7√3×7√3 are formed for the Sb coverages around one monolayer.