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To extend the input power range and increase RF sensitivity for energy harvesting in medical implant communication service (MICS) band, a high quality (Q) matching network is applied in 403 MHz rectifier circuit. In this proposed design, a finite unload Q series inductor is placed between a pair of shunt capacitors to enhance the overall load Q factor of impedance matching network when compared with conventional type. By using lump components, the compact size of rectifier is 1.4 cm x 0.8 cm that suitable for medical implant devices in human body tissue. The compact-size rectifier has the measured efficiency $(\eta)$ where the input power range for $\eta$ above 50.1 % is from -8.1 dBm (RF sensitivity) to 11.5 dBm and thus, the input power range of 19.6 dB is achieved. At 5 dBm the peak efficiency is 68.1 %.

CdSe/ZnS core–shell structured nano-crystal quantum dots (QDs) are ideal candidates for light-emission applications due to their high quantum efficiency, narrow-band, and particle-size-tunable photoluminescence. In particular, their small size results in the quantum confinement of semiconductor nano-crystals, which widens their energy gaps. In general, structural analyses of QDs using a transmission electron microscope (TEM) are very important due to the significantly small size of QDs. We were able to obtain structural information of CdSe/ZnS core–shell QDs using nano-beam diffraction by controlling the nano-probe of the dark field scanning TEM (DF-STEM) mode and strain analysis with high-resolution TEM (HRTEM)/STEM images. Furthermore, we could clearly distinguish the interface between the CdSe core and the ZnS shell from the strain analysis with the HRTEM/STEM images.

We suggest uncertainty compensation methods for the quantification of nanoscale indentation using atomic force microscopy (AFM). The main error factors in the force–distance curves originated from the difference between theoretical and real shape of AFM tip during nanoscale indentation measurements. For the uncertainty compensations of tip shapes and misalignment of loading axis, we applied the enhanced tip geometry function and Y-scanner moving to the AFM measurements. Three different materials such as Si wafer, glass, and Au film were characterized with these compensation methods. By applying compensation methods, our results show the decreased values from 167% to 39% below 100 nm indenting depth compared with the literature values. These compensation methods applied to thin films will show the advanced quantitative analysis of hardness measurements using nanoscale indenting AFM.

Due to the large differences in the lattice constants and the thermal expansion coefficients between GaN and Si, GaN growth on a Si substrate usually leads initially to high defect densities and cracks. If high-quality GaN films on Si substrate are to be obtained, it is essential to understand the different growth characteristics of GaN layers grown on Si and on sapphire. In this study, the GaN specimens were grown on sapphire and Si (111) substrates with AlGaN and AlN buffer layers, respectively, by metalorganic chemical vapor deposition (MOCVD). Using transmission electron microscopy (TEM) and micro-Raman spectroscope, we carried out a comparative investigation of GaN growth by characterizing lattice coherency, defect density, and residual strain. These analyses revealed that the GaN layers grown on Si have much residual tensile strain and that strain has an effect on the formation of InGaN/GaN multiple quantum wells (MQWs) above the GaN layers.

The authors present the blue-shift of Raman 2D and G peak of a single layer graphene film, which is fabricated via chemical vapor deposition, on the relatively even Cu foil domain with nearly uniform thickness. This can be interpreted that rather mechanically compressive strain is exerted between graphene and the even Cu domain compared to the uneven. We observe that relaxing compressive strain to minimize the perturbation from Cu surface to the graphene film by virtue of the uneven Cu domain has a critical role in forming a suspended graphene. Furthermore, mechanical strain influence derived from the underlying substrate morphology can be suggested as one of the crucial elements in evaluating high quality graphene film considering suspended shape.

CdSe/ZnS core–shell structured nano-crystal quantum dots (QDs) are ideal candidates for light-emission applications due to their high quantum efficiency, narrow-band, and particle-size-tunable photoluminescence. In particular, their small size results in the quantum confinement of semiconductor nano-crystals, which widens their energy gaps. In general, high resolution imaging analyses of QDs using a transmission electron microscope are very difficult due to their significantly small size. Successful imaging depends on the capabilities of TEM equipment and the contrast of the QDs sample relative to the supporting film. In this work, all imaging analyses were performed on a TEM equipped with a probe Cs corrector. The samples for observing QDs were prepared by drying each QDs solution on a lacey carbon Cu (300 mesh) grid previously coated with an ultra-thin graphene monolayer (thickness = 0.3 nm), due to the need to minimize the effect of the supported film.

The microstructure of abnormal grains in Al-doped ZnO (AZO) films using a seed layer was examined with the aim of enhancing the performance of transparent conducting oxides in thin film solar cells. The AZO films were prepared by DC-pulsed magnetron sputtering using a two-step process. The seed layer was deposited on a glass substrate under an Ar/O2 atmosphere with a gas flow ratio of 24/1, and the bulk layer was formed on the seed layer in pure Ar. The microstructural properties of the AZO films were investigated by transmission electron microscopy (TEM), fast Fourier transform simulation, and strain analysis with high-resolution TEM images. The TEM revealed peculiar microstructures on the AZO film showing abnormal grains and a rough surface. The AZO seed layer was formed at a thickness of 50 nm, and two types of grains with columnar and hillock structures were formed on the seed layer. Elemental analysis using energy dispersive X-ray measurement showed that the abnormal grains contained more metallic elements (Al and Zn) than the normal region with columnar structure in the AZO film. The analysis of fast Fourier transform images of each region showed that the crystal structures of the normal and abnormal grains were the same, whereas the abnormal grain had a different growth orientation from that of the normal region. Copyright © 2012 John Wiley & Sons, Ltd.

We studied the growth mechanism of Al-doped ZnO (AZO) films using seed layers for enhancing the performance of transparent conducting oxides (TCOs) in the thin film solar cells. We carried out two-step processes for the deposition of AZO films. Seed layers were deposited on glass substrate as a function of Ar/O2 gas flow ratio. We show the results of our investigation on the micro-structural properties of AZO seed layers using transmission electron microscopy (TEM). The elemental composition and electronic structure changes with the deposition conditions were examined using energy dispersive X-ray (EDX) and reflective electron energy loss spectroscopy (REELS). The optical and electrical characteristics of AZO film using the seed layer with Ar/O2 = 9/1 show a high haze value of 88% at 500 nm and a resistivity value of 3.7 × 10 Ω·cm.

Aging phenomena of plasma polymer films were studied by using the surface analysis techniques of contact angle measurement, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOFSIMS), and atomic force microscopy (AFM). The polymer films were grown on an aluminum substrate by using a plasma polymerization method from a gas mixture of acetylene and helium, and the films were subsequently modified to have a hydrophilic surface by oxygen plasma treatment. Aging of the polymer films was examined by exposing the samples to water and air environments. The aging process increased the hydrophobicity of the surface, as revealed by an increase in the advancing contact angle of water. XPS analysis showed that the population of oxygen-containing polar groups increased due to the uptake of oxygen during the aging, whereas TOF-SIMS analysis revealed a decrease in the polar group population in the uppermost surface layer. The results suggest that the change in surface property from hydrophilic to hydrophobic nature results from the restructuring of polymer chains near the surface, rather than compositional change of the surface. Oxidative degradation may enhance the mobility and the restructuring process of polymer chains.

The threading dislocation (TD) density in GaN films grown directly on flat sapphire substrates is typically >10 10 /cm 2 , which can deteriorate the properties of GaN-based LEDs significantly. This paper reports an approach to reducing the TD density in a GaN layer using a variety of patterned sapphire substrates (PSS). A cone-shaped PSS produced by metal organic chemical vapor deposition (MOVCD) was used for GaN deposition. Three types of GaN specimens were prepared at the initial nucleation stage, middle growth stage and final growth stage. The TDs generated on the cone-shaped PSS were analyzed by transmission electron microscopy (TEM) and a strain mapping simulation using HRTEM images, which evaluated the residual strain distribution. A large number of TDs were generated and the residual strain by the lattice distortions remained above the top of the cone-shaped regions. However, no TDs and residual strain were observed at the slope of the cone-shaped regions. This might be due to the formation of a GaN layer by lateral overgrowth at the slope of the cone-shaped regions, resulting in less lattice mismatch and incoherency between the GaN and sapphire. In conclusion, the TD density in the GaN layer could be reduced significantly, approximately 10 7 /cm 2 , using the cone-shaped PSS.

The formation characteristics of the inversion domains in p-GaN and p-AlGaN layers were investigated by using transmission electron microscopy (TEM). The inversion domains induced by Mg-doped p-type GaN (p-GaN) and p-AlGaN layers were formed on a sapphire substrate by using a metalorganic chemical vapor deposition (MOVCD) method. The induced inversion domains were analyzed by using high-resolution TEM (HRTEM) and convergent beam electron di raction (CBED) and the residual strain distribution was evaluated by using a strain mapping simulation. The results revealed that pyramidal defects of various sizes were formed at the p-GaN/p-AlGaN interface. Also, a large number of inversion domains were observed to be initiated exclusively on (0002) plane of the pyramidal defects, which were above 10 nm toward the [000 1] direction, resulting in a rough, island-shaped p-GaN surface due to the inhibition of GaN growth by the inversion domains. In this study, the formation characteristics of inversion domains were correlated with the in uence of structural defects existing at the p-GaN/p-AlGaN interface.

With application of the current transport enhanced layer (CTEL) on the top of p-type GaN, we optimized process conditions, which show the contact resistance of 1.43x10–3 Ω·cm2, using ITO contact layer that has advantages in the enhancement of light extraction efficiency. High-resolution near edge X-ray absorption spectroscopy was used to investigate the interface reaction between GaN / CTEL and ITO layers. Interstitial molecular N2 was directly observed by vibrationally resolved N'K-edge absorption spectroscopy. It is suggested that GaN was chemically changed to gallium oxide (Ga2O3) and nitrogen molecule (N2) [2Ga-N + 3/2 O2 => Ga2O3+N2] during annealing process, and this newly formed layer makes depletion width narrowing for the tunneling properties for the ohmic contact. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The microstructural variation and the interdiffusion of Pt (80 nm)/Ti (70 nm)/SiO2/Si during annealing in O2 were investigated using Auger electron spectroscopy, x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. While the as-deposited and 400 °C annealed samples showed well-defined layer structures without any significant interfacial reaction, the degree of oxidation remarkably increased with increasing temperature above 500 °C. The PtTi alloy phase with Pmma structure (AuCd type) was observed from the 500 °C annealed sample. Drastic interdiffusion occurring above 600 °C changed the Pt/Ti bilayer into a very entangled structure. Some TiO2 phases were exposed to the ambient between Pt hillocks. In addition, a small amount of Pt-silicide was found near the TiOx/SiO2 interface.

Comparison has been made between the microstructures and electrical properties of Pb0·95La0·05TiO3 (PLT) thin films deposited on bare (100)MgO and on Pt/(100)MgO. Nearly perfect epitaxial PLT was grown on (100)MgO. (100)-oriented Pt film was obtained via coalescence of Pt islands formed on MgO. Highly c-axis oriented PLT thin film was successfully grown on the Pt bottom electrode with an electrically conductive network structure. High detectivity of 3·5 × 108 and 2·6 × 108 cm√Hz/W was obtained at 30 Hz without any poling treatments from the PLT/MgO- and PLT/Pt/MgO-based infrared detectors, respectively.

We demonstrate low-temperature growth and direct transfer of graphene-graphitic carbon films (G-GC) onto plastic substrates without the use of supporting materials. In this approach, G-GC films were synthesized on copper layers by using inductively coupled plasma enhanced chemical vapor deposition, enabling the growth of few-layer graphene (G) on top of Cu and the additional growth of graphitic carbon (GC) films above the graphene layer at temperatures as low as 300 °C. The patterned G-GC films are not easily damaged or detached from the polymer substrates during the wet etching and transfer process because of the van der Waals forces and π-π interactions between the films and the substrates. Raman spectroscopy reveals the two-dimensional hexagonal lattice of carbon atoms and the crystallinity of the G-GC films. The optical transparency and sheet resistance of the G-GC films are controlled by modulating the film thickness. Strain sensors are successfully fabricated on plastic substrates, and their resistance modulation at different strains is investigated.

The ZnO:Al films were prepared using a two-step process through the control of oxygen pressure by DC-pulsed magnetron sputtering. The seed layers were prepared with various Ar to oxygen pressure, and the bulk layers were deposited under pure Ar. At the seed-layer condition of Ar/O 2 = 24/1 (Ar rich), the seed layer showed grains that led to the formation of hillock, and the grains of seed layer were seem to act as nucleation sites for columnar growth of bulk layer. While, at the seed-layer condition of Ar/O 2 =4/1 (oxygen rich), grains show large lateral growth with a nonuniform distribution, and a number of dislocations are shown in grains. As oxygen pressure during the deposition of seed layer increased, the decrease of local strain (or the increase of crystallinity) was observed. The etched surface showed the crater-like structure and the abrupt morphology change appeared at high oxygen pressure, which was likely due to nonuniform grain structure and/or the decrease in the number of chemical attack sites by the drastic decrease of grain boundary. The haze values increased with increasing oxygen pressure, which was explained by the change of crater size, as shown in the AFM image.

We investigated the amorphous indium gallium zinc oxide (IGZO) based TFT interface properties using synchrotron radiation analysis. Near edge x-ray absorption fine structure shows the presence of N2 molecules between gate dielectric layer and active channel layer. The physical damage enhanced by the sputtering process was the origin of the device degradation evolving molecular state N2.

The Ni silicide-mediated phase transformation of amorphous to crystalline silicon (c-Si) was studied using transmission electron microscopy. Amorphous silicon (a-Si) films coated with very thin Ni layer (∼10-1Å) were annealed at various temperatures. Randomly oriented NiSi2 precipitates were observed in the Ni deposited a-Si film annealed at 400°C. The nucleation of the epitaxial c-Si has occurred on the {111} faces of the octahedral NiSi2 precipitate at 430°C and then caused to the variation in the shape of the NiSi2 precipitates. During the growth of c-Si, the needle-like morphology developed from the migration of NiSi2 precipitates through the a-Si matrix leaving a trail of c-Si. The collision of a migrating NiSi2 precipitate with a stationary NiSi2 precipitates in the a-Si film gave rise to the change in the morphology of the growing Si grain and the formation of additional c-Si needles on variants of the direction.

We employ electrostatic force microscope (EFM) techniques to explore local electrical properties of suspended graphene on Cu foil, SiO2/Si and PET substrate. By using electrical modulation of amplitude in a tapping mode atomic force microscope tip, we can obtain distinguished electrostatic force amplitude mapping of graphene on various substrates. In particular, at nano-valley domains on Cu and a SiO2/Si surface, relatively weaker electrostatic attractive interaction is observed than at nano-peak domains. In SiO2/Si, we find that electrostatic force distribution of graphene still follows the substrate surface morphology. Furthermore, employing EFM to graphene on a PET system can be suggested as a facile tool to investigate electrical performance of graphene.

We can experimentally identify the layer-layer breathing mode and the other out-of-plane transverse acoustic phonon modes of a few layered graphene via employing z-polarized incident field formed at Au nanoparticle-Au film junctions. The observed out-of-plane mode phonon at ∼150 cm−1 and other transverse acoustic phonon type defect modes from 300 cm−1 to 700 cm−1 can be readily explored. Not only for the normally used optical method using focused plane wave but also direct applying the z-directional electromagnetic field on graphene will be expected for more detailed out-of-plane phonon characterization of graphene.

We present that the Raman 2D and G peak of graphene film fabricated via chemical vapour deposition (CVD) blue-shifts on the relatively even Cu foil domain, showing a rather compressive strain effect compared to the uneven domain. We experimentally figure out that the relaxing compressive strain, to minimize the adhesive interaction between the graphene and the Cu surface, has one of the critical roles in forming suspended few-layered graphene. The nanoscopic conductance investigation also reveals that the current flow is dominantly measured at the uneven nano-terrace domains rather than at the even, further signifying the importance of a detailed underlying Cu surface morphology.

We examine local electrostatic force distribution of polyethylene terephthalate (PET) film surface before and after transferring graphene in order to compare the influence of local electrostatic interaction between graphene and PET film in terms of the sheet resistance value of deposited graphene. By using the electrical modulation of amplitude in a tapping mode AFM tip, we can obtain the distinguished electrostatic force amplitude mapping of graphene. We determine that different electrostatic attractive interactions between Au-coated tip and bare PET are present and the observed difference can affect the graphene formation and electrical performance, which correlates with the sheet resistance difference.

The evolution of the shunt path on the performance of Si-based thin film solar cells with an glass/Al-doped ZnO (AZO)/amorphous (a)-Si:H/a-SiGe:H/Al was investigated by conductive atomic force microscopy, electroluminescence measurement, and transmission electron microscopy. AZO films were highly textured for the light management before the deposition of absorption layers. The cell performance was found to be strongly dependent on the existence of nanocracks formed in a-Si:H/a-SiGe:H layers. The defects by nanocracks are expected to attribute to the leakage current in the cells. The authors introduce two types of shunt path evolution modes: pinhole defects (type A) and highly textured groove of AZO film (type B). Both crack defects by types A and B induced high leakage current, leading to a relatively reduced fill factor on the performance.

ZnO:Al films were prepared using a two-step process involving the control of oxygen pressure. The seed layers were deposited under various Ar to oxygen pressure ratios, and the bulk layers were prepared under pure Ar. The growth mode was systematically examined and clearly different microstructures were shown according to the deposition condition of the seed layer. With increase of oxygen pressure, the crystallinity and the degree of (002) texturing increased. The haze values of etched films also increased with increasing oxygen pressure, which was explained by the grain-structure of as-deposited films.

Reconstruction and exaggerated grain growth (EGG) behaviors of redeposited MgO layer were observed and analyzed theoretically with the addition of dopant and MgO seed particle. The reconstruction and EGG are closely correlated with the driving force for nucleation and growth, interface energy and initial size distribution of MgO protective layer and this is believed to be caused by the formation of charged clusters in the plasma spaces during discharge in AC-PDPs.

We report the optimized process and Ohmic mechanism for an indium tin oxide (ITO)/p-GaN Ohmic contact. The current transfer enhanced layer (CTEL) on the top of p-type GaN was introduced to improve the Ohmic properties. The samples were annealed at temperatures in the range of 400 ∼ 800 ◦C under gas ambients of 0 (i.e., pure N2), 0.1, 0.2, and 0.5 % O2/N2 ratio. A small amount of O2 addition shows much lower contact resistance than the pure N2 only ambient while a high O2/N2 ratio exhibits an abruptly increasing the contact resistance and operating voltage. The contact resistance of the ITO/(CTEL)/p-GaN layer shows the best value of 1.43 × 10−3 ohm·cm at the annealing temperature of 650 ◦C and a 0.1 % O2/N2 gas ambient. High resolution near edge X-ray absorption spectroscopy (NEXAFS) shows that more interstitial N2 molecules were formed from the ITO/CTEL interfaces with increasing O2/N2 ratio. From the NEXAFS results, the high contact resistance could be explained with a possible reaction, 2GaN + 3/2O2→Ga2O3 + N2, during the annealing process. It could be suggested that the newly formed oxide layer makes the depletion width more narrowing for the Ohmic contact with a tunneling junction. However, the thick oxide layer formed at the high O2/N2 ratio might keep the hole carriers from transporting to the electrode.

The growth characteristics of a GaN layer deposited on a cone-shaped patterned sapphire substrate (PSS) by using metalorganic chemical vapor deposition (MOVCD) were observed by transmission electron microscope (TEM) to investigate the influence of cone-shaped PSS on the GaN layer. The GaN/sapphire interfaces were analyzed by using high-resolution TEM (HRTEM) and convergent beam electron diffraction (CBED), and the residual strain was evaluated by measuring the variation of the lattice parameters quantitatively. From the TEM images, a large number of threading dislocations were found above the flat region of the GaN/sapphire interface. In contrast, only a few threading dislocations were identified above the cone-shaped region. The HOLZ pattern analysis revealed that the lattice parameter of the GaN layer was lower above the flat region of the GaN/sapphire interface compared with the cone-shaped region, and the difference was estimated to be about 0.1 %. This may be attributed to the formation of a GaN layer by the lateral overgrowth above the cone-shaped region, resulting in less lattice mismatch and incoherency between the GaN layer and the sapphire substrate.