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The commercialization of transistors capable of both switching and amplification in 1960 resulted in the development of second-generation computers, which resulted in the miniaturization and lightening while accelerating the reduction and development of production costs. However, the self-resistance and the resistance used in conjunction with semiconductors, which are the basic principles of computers, generate a lot of heat, which results in semiconductor obsolescence, and limits the computation speed (clock rate). In implementing logic operation, this paper proposes the concept of Structure-based Computer which can implement NOT gate made of semiconductor transistor only by Structure-based twist of cable without resistance. In Structure-based computer, the theory of ’inverse signal pair’ of digital signals was introduced so that it could operate in a different way than semiconductor-based transistors. In this paper, we propose a new hardware called Structure-based computer that can solve various problems in semiconductor computers only with the wiring structure of the conductor itself, not with the silicon-based semiconductor. Furthermore, we propose a deep-priority exploration-based simulation method that can easily implement and test complex Structure-based computer circuits. Furthermore, this paper suggests a mechanism to implement optical computers currently under development and research based on structures rather than devices.

Memristive systems can provide a novel strategy to conquer the von Neumann bottleneck by evaluating information where data are located in situ. To meet the rising of artificial neural network (ANN) demand, the implementation of memristor arrays capable of performing matrix multiplication requires highly reproducible devices with low variability and high reliability. Hence, we present an Ag/CuO/SiO2/p-Si heterostructure device that exhibits both resistive switching (RS) and negative differential resistance (NDR). The memristor device was fabricated on p-Si and Indium Tin Oxide (ITO) substrates via cost-effective ultra-spray pyrolysis (USP) method. The quality of CuO nanoparticles was recognized by studying Raman spectroscopy. The topology information was obtained by scanning electron microscopy. The resistive switching and negative differential resistance were measured from current&ndash, voltage characteristics. The results were then compared with the Ag/CuO/ITO device to understand the role of native oxide. The interface barrier and traps associated with the defects in the native silicon oxide limited the current in the negative cycle. The barrier confined the filament rupture and reduced the reset variability. Reset was primarily influenced by the filament rupture and detrapping in the native oxide that facilitated smooth reset and NDR in the device. The resistive switching originated from traps in the localized states of amorphous CuO. The set process was mainly dominated by the trap-controlled space-charge-limited, this led to a transition into a Poole&ndash, Frenkel conduction. This research opens up new possibilities to improve the switching parameters and promote the application of RS along with NDR.

The success of molecular therapies targeting specific metabolic pathways in cancer is often limited by the plasticity and adaptability of metabolic networks. Here we show that pharmacologically induced lipotoxicity represents a promising therapeutic strategy for the treatment of hepatocellular carcinoma (HCC). LXRα-induced liponeogenesis and Raf-1 inhibition are synthetic lethal in HCC owing to a toxic accumulation of saturated fatty acids. Raf-1 was found to bind and activate SCD1, and conformation-changing DFG-out Raf inhibitors could disrupt this interaction, thereby blocking fatty acid desaturation and inducing lethal lipotoxicity. Studies in genetically engineered and nonalcoholic steatohepatitis-induced HCC mouse models and xenograft models of human HCC revealed that therapies comprising LXR agonists and Raf inhibitors were well tolerated and capable of overcoming therapy resistance in HCC. Conceptually, our study suggests pharmacologically induced lipotoxicity as a new mode for metabolic targeting of liver cancer. Zender, Dauch and colleagues demonstrate that pharmacologically induced lipotoxicity by activating LXRα and Raf-1 inhibition provides a metabolic therapeutic strategy for hepatocellular carcinoma.

In this work, Cu doped SnS2 nanoflakes were synthesized through a simple hydrothermal method. The influence of Cu doping on the structural, optical and electrical properties of SnS2 were investigated in detail. Optical properties explores the Cu doping in SnS2 crystal lattice to result with a red-shift in absorption spectrum, which benefits visible-light absorption. Photodiodes were further fabricated by spin coating Cu doped SnS2 nanoflakes on p-type silicon (Si). Electrical and photoelectrical parameters of Cu doped SnS2 nanoflakes were determined by studying their impedance and current–voltage (I–V) characteristics, respectively. The diodes were found to exhibit excellent rectifying behavior and good sensitivity on par to pristine photodiodes. Impedance results identified the resistance of device to reduce considerably on Cu doping. The enhanced photoelectrical properties of the heterojunctions has been ascribed to Cu ions, which act as effective dopant and contribute to the varied carrier concentration in SnS2. Finally the obtained results suggest the potential of Cu-doped SnS2 for application in photodetection and sensors applications.

The demand for low-cost high efficient photoelectronic devices tends to drive the present need for investigations on advanced multi-functional semiconducting nanostructures. In this regard, the physico-chemical traits of sonochemically processed ZnTe nanostructures and hydrothermally grown ZnO nanostructures were studied using Raman, UV–vis absorbance, X-ray photoelectron spectroscopy and high resolution microscopic tools. The p-n ZnTe/ZnO heterojunctions were then fabricated via spin casting a colloidal ZnTe suspension on periodically aligned ZnO nanowires and investigated for their photoelectronic functionalities. The current-voltage (I-V) characteristics revealed an obvious rectifying behaviour with the forward current and rectification ratio getting improved on lowering the threshold voltages. The series resistance of the diodes were additionally studied using the dV/dlnI derivate plots. The stability of the diodes were also affirmed using their time-dependent photoresponse characteristics, which actually suggested the improved and effective separation of photo generated electron hole pairs across the interface. Finally, the ZnTe/ZnO heterojunction behaviour was assimilated using the electrochemical impedance spectroscopic (EIS) results that were studied individually for ZnTe and ZnO nanostructures and collectively across ZnTe/ZnO heterostructure.

MoS2/reduced graphene oxide (rGO) nanocomposites were synthesized using an ultrasonic pretreatment with a single-stage hydrothermal and reduction process. Self-assembled MoS2 layers in the rGO matrix were obtained. The effect of quantum confinement in the structure, controlled by the degree of reduction of graphene oxide and the size of the 2D MoS2 nanocrystals, made it possible to obtain tunable optical absorption. MoS2/rGO layered nanocomposites exhibit a wide UV-IR absorption in the wavelength range from 280 nm to 973 nm, which is attractive for highly efficient multiband solar cells and advanced photonics.

Tin monosulfide (SnS) nanostructures have attracted huge attention recently because of their high absorption coefficient, high photoconversion efficiencies, low energy cost, ease of deposition, and so on. Here, in this paper, we report on the low-cost hydrothermal synthesis of the self-assembled SnS nanoflake-like structures in terms of performance for the photodetectors. High-performance photodetectors were fabricated using SnS nanoflakes as active layers and graphene as the lateral electrodes. The SnS photodetectors exhibited excellent photoresponse properties with a high responsivity of 1.7 × 104 A/W and have fast response and recovery times. In addition, the photodetectors exhibited long-term stability and strong dependence of photocurrent on light intensity. These excellent characteristics were attributed to the larger surface-to-volume ratio of the self-assembled SnS nanoflakes and the effective separation of the photogenerated carriers at graphene/SnS interfaces. Additionally, a flexible photodetec...

Nowadays, solid-state inorganic-organic hybrid solar cells based on one-dimensional (1D) inorganic semiconducting nanostructures and organic polymers are believed to offer convincing solutions for the realm of next generation solar cells. In this regard, 1D ZnCdS nanowire (NW) arrays were fabricated on transparent conducting substrates through a catalyst free co-evaporation method and their wurtzite structural characteristics, 1D morphological layout and valence state/composition were studied in detail using X-ray diffraction, high-resolution electron microscopy and X-ray photoelectron spectroscopy, respectively. The existence of deep level traps and optical band gap of ZnCdS NWs were additionally studied using room-temperature cathodoluminescence and UV–vis absorbance measurements. The inorganic-organic hybrid cells were then fabricated using these NWs via spin coating poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonate) based polymers. The morphological dissemination of the polymer deposits on NWs were also studied individually by electron microscopy. The solar cell (J-V) characteristics of the fabricated architectures were investigated at room-temperature and as a function of temperature and different intensities of incident light irradiation. The trap energy of the devices was noted to decrease from 68.1 to 40.7 eV, suggesting the active role of trap sites that could have originated from the surface defects and other structural disorders across the hybrid heterostructures.

MoS2 2D nanosheets (NS) with intercalated 0D quantum dots (QDs) represent promising structures for creating low-dimensional (LD) resistive memory devices. Nonvolatile memristors based 2D materials demonstrate low power consumption and ultrahigh density. Here, the observation of a photoinduced phase transition in the 2D NS/0D QDs MoS2 structure providing dynamic resistive memory is reported. The resistive switching of the MoS2 NS/QD structure is observed in an electric field and can be controlled through local QD excitations. Photoexcitation of the LD structure at different laser power densities leads to a reversible MoS2 2H-1T phase transition and demonstrates the potential of the LD structure for implementing a new dynamic ultrafast photoresistive memory. The dynamic LD photomemristive structure is attractive for real-time pattern recognition and photoconfiguration of artificial neural networks in a wide spectral range of sensitivity provided by QDs.

In this paper, a photodetector based on arrayed CdTe microdots was fabricated on Bi coated transparent conducting indium tin oxide (ITO)/glass substrates. Current-voltage characteristics of these photodetectors revealed an ultrahigh sensitivity under stress (in the form of force through press) while compared to normal condition. The devices exhibited excellent photosensing properties with photoinduced current increasing from 20 to 76 &mu, A cm&minus, 2 under stress. Furthermore, the photoresponsivity of the devices also increased under stress from 3.2 &times, 10&minus, 4 A/W to 5.5 &times, 3 A/W at a bias of 5 V. The observed characteristics are attributed to the piezopotential induced change in Schottky barrier height, which actually results from the piezo-phototronic effect. The obtained results also demonstrate the feasibility in realization of a facile and promising CdTe microdots-based photodetector via piezo-phototronic effect.

In this work, we report on single CdS nanobelts (NB), Multi-walled carbon nanotube (MWCNT)/CdS NB and MWCNT:Cu/CdS NB based hybrid devices for photodetector applications. The electrical properties of the MWCNT:Cu/CdS NB devices tends to exhibit excellent photo to dark current ratio and a higher photoresponse of 7.5 times than that of pristine CdS device. The results also suggest MWCNT:Cu/CdS NB for potential application in photodetectors that require high photocurrent to dark current ratio and remarkable stability.

4H-SnS2 layered crystals synthesized by a hydrothermal method were used to obtain via liquid phase exfoliation quantum dots (QDs), consisting of a single layer (SLQDs) or multiple layers (MLQDs). Systematic downshift of the peaks in the Raman spectra of crystals with a decrease in size was observed. The bandgap of layered QDs, estimated by UV-visible absorption spectroscopy and the tunneling current measurements using graphene probes, increases from 2.25 eV to 3.50 eV with decreasing size. 2–4 nm SLQDs, which are transparent in the visible region, show selective absorption and photosensitivity at wavelengths in the ultraviolet region of the spectrum while larger MLQDs (5–90 nm) exhibit a broad band absorption in the visible spectral region and the photoresponse under white light. The results show that the layered quantum dots obtained by liquid phase exfoliation exhibit well-controlled and regulated bandgap absorption in a wide tunable wavelength range. These novel layered quantum dots prepared using an inexpensive method of exfoliation and deposition from solution onto various substrates at room temperature can be used to create highly efficient visible-blind ultraviolet photodetectors and multiple bandgap solar cells.

A graphene-InGaN Schottky junction has been successfully fabricated by transferring graphene layers onto n-type In0.23Ga0.77N/GaN/Al2O3 substrates. Current–voltage (I–V) measurement across the junction demonstrates the rectifying behaviour. Temperature dependent I–V characteristics in a range of 10 K to 300 K reveal that the charge transport mechanism is dominated by thermionic emission. Also, it is observed that the charge-transfer induced variation of Fermi energy of graphene affects the flow of current. This graphene/InGaN junction shows electroluminescence (EL) characteristics under a forward bias, producing bright blue emission (430 nm) at room temperature. As the temperature increases, the EL peak is shifted to a lower energy with a reduced peak intensity due to the increased nonradiative recombination rate. The dependence of EL intensity on the current of the graphene/InGaN junction confirms the band-to-band recombination mechanism in the InGaN layer by the bimolecular radiative recombination. Therefore, the observed results provide an insight for implementing graphene based Schottky-junction devices with tunable emission by utilizing the variable bandgap of the InGaN layer.

One-dimensional ZnO nanorods were grown vertically on a (100) Si substrate using a vapor phase transport method. Following the fabrication of ZnO nanorods, Si layers were deposited by rapid thermal chemical vapor deposition (RTCVD) directly on the ZnO nanorod/Si (100) substrate. Field emission scanning electron microscopy revealed that a Si/ZnO nanorod coaxial heterostructure were synthesized vertically oriented along the (002) plane on a Si substrate. X-ray diffraction, Energy dispersive X-ray and Raman spectroscopy revealed that the ZnO nanorods were single crystals with a hexagonal structure, and grew with a c-axis orientation perpendicular to the Si substrate, whereas the Si layer was poly-silicon with cubic structure. These results demonstrated the Si/ZnO nanorod coaxial heterostructure were synthesized successfully on a (100) Si substrate and the ZnO nanorod enables the synthesis of a vertically grown well-aligned Si/ZnO coaxial nanorod heterostructure.

The response of the near-band-edge photoluminescence (PL) emission of ZnO thin films to annealing and the electric field’s action was investigated. These processes separately caused similar changes in the PL spectrum. The donor bound exciton emission at 3.36 eV, which is attributed to bulk defects, demonstrated invariance to any exposure, while the intensity of the 3.33-eV emission line decreased after annealing in nitrogen gas and was restored after annealing in an oxygen atmosphere. On the other hand, application of an electrical field during laser illumination resulted in the same change in the PL spectrum. The transition of defects related to the 3.33-eV emission from a radiative to a non-radiative state (and inversely) through the capture (release) of electrons was proposed as the mechanism responsible for the observed changes in the optical properties. The desorption of oxygen from the surface of the ZnO film during annealing in N2 or the motion of photogenerated electrons toward the surface during laser illumination were suggested to be the cause of this capture process.

We demonstrate the evolution of GaN films on novel langasite (LGS) substrate by plasma-assisted molecular beam epitaxy, and assessed the quality of grown GaN film by comparing the experimental results obtained using LGS, sapphire and silicon (Si) substrates. To study the substrate effect, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) spectra were used to characterize the microstructure and stress states in GaN films. Wet etching of GaN films in KOH solution revealed that the films deposited on GaN/LGS, AlN/sapphire and AlN/Si substrates possess Ga-polarity, while the film deposited on GaN/sapphire possess N-polarity. XRD, Raman and PL analysis demonstrated that a compressive stress exist in the films grown on GaN/LGS, AlN/sapphire, and GaN/sapphire substrates, while a tensile stress appears on AlN/Si substrate. Comparative analysis showed the growth of nearly stress-free GaN films on LGS substrate due to the very small lattice mismatch (~3.2%) and thermal expansion coefficient difference (~7.5%). The results presented here will hopefully provide a new framework for the further development of high performance III-nitride-related devices using GaN/LGS heteroepitaxy.

Herein, we report the self-aligned growth of GaN nanorods on different orientations of sapphire like c-, a-, r- and m-plane substrates by hydride vapor phase epitaxy. Vertical c-axis orientation of GaN NRs is obtained on c-plane [0001] and a-plane $$ \left[ { 1 1\bar{2}0} \right] $$ sapphire and a skew or inclined NRs on r-plane, and inclined intertwined but self-aligned NR array was formed on m-plane sapphire. GaN (002) and (004) peaks were obtained on c- and a-plane sapphire, whereas (110), (103), and (103) only were observed on r- and m-planes, respectively. In the case of r- and m-plane-grown GaN, A1 transverse optical mode is dominant, and the A1 longitudinal optical mode is suppressed. Conversely, in the case of c- and a-plane, it is reversed. The probable reason is the optical mode vibrations difference along the differently inclined NRs surfaces. In addition, the specimen exhibits surface optical modes too. The optical behavior of GaN NR on m-sapphire shows an intensity variation when measured in different angular rotations of the specimen by photoluminescence which is because of the higher area of excitation in the case of axial surfaces and lower area of excitation in radial surface. Their epitaxial crystallographic relationship with the substrates and the reasons for the self-aligned orientations are discussed. The anomalies found in the optical behavior are attributed to Raman antenna effect and so on. The self-aligned intertwined GaN NRs find suitable applications in polarizer.

Potassium-doped ZnO thin films electrodeposited on indium tin oxide (ITO) coated glass substrates exhibited ferroelectric behavior with a remnant polarization of 0.2 µC/cm2. Especially, wave forms showing the applied input voltage Vi and output voltage Vo were obtained for Al/ZnO:K/ITO structure. It exhibits a superposition of Vi (input) and Vo (output) signal from Al/ZnO:K/ITO structure with a clear phase shift between the two wave forms which again confirms that the observed ferroelectric hysteresis curve is not related to leaky dielectric materials. The current–voltage characteristics of Al/ZnO:K/ITO structures measured for several cycles revealed bi-stable switching characteristics. The reproducible bi-stable switching characteristics for the mentioned structures had good retention in one particular resistance state. Around one order of switching was realized between low and high resistance states. The switching property thought to be polarization induced originating out from the ferroelectric properties of the potassium doped ZnO thin film. The switching between ZnO:K/ITO interface is assumed to be critical for stability in switching for several cycles. Possible application of this structure in non-volatile memories is explored.

We report the epitaxial growth of c-plane GaN films on a novel langasite (La3Ga5SiO14, LGS) substrate by plasma-assisted molecular beam epitaxy. The in-plane epitaxial relationship and the structural properties of GaN films on an LGS substrate were investigated using in situ reflective high energy electron diffraction (RHEED), high resolution X-ray diffraction (HR-XRD) and Raman spectroscopy. The in-plane epitaxial relationship between GaN and LGS determined using RHEED pattern was found to be GaN[100]//LGS[210] and GaN[110]//LGS[140]. HR-XRD results confirmed the exact epitaxial relationship, and showed that six reflection peaks of GaN(102) were shifted around 19° from those of LGS(102). Raman analysis revealed that a minute compressive strain still existed in the GaN film due to the very small lattice mismatch between GaN and LGS. The results obtained in this study demonstrate that the nearly lattice-matched LGS can be a promising and futuristic substrate material for the growth of GaN, and it is foreseen that our results could be a reference for the further development of high performance nitride-based devices.

Colloidal zinc telluride (ZnTe) nanostructures were successfully processed through a simple and facile ultrasonic (sonochemical) treatment for photoelectronic applications. The particle-like morphological features, phase and nature of valence state of various metal ions existing in ZnTe were examined using electron and X-ray photoelectron spectroscopic tools. Raman spectroscopic measurements revealed the dominance of exciton-phonon coupling and occurrence of TeO2 traces in ZnTe through the corresponding vibrations. Optical bandgap of the ZnTe suspension was estimated to be around 2.15eV, authenticating the direct allowed transitions. The p-type electrical conductivity and charge carrier density of ZnTe were additionally estimated from the Bode, Nyquist and Mott-Schottky type impedance plots. The photoelectrical properties of ZnTe were investigated by fabricating p-ZnTe/n-Si heterostructures and studying their corresponding current-voltage characteristics under dark and white light illumination. The diodes revealed excellent rectifying behaviour with significant increase in reverse current under illumination. The stability of the devices were also affirmed through the time-dependent photoresponse characteristics, which actually suggested the improved and effective separation of photo generated electron hole pairs across the integrated heterojunctions. The obtained results also augment the potential of sonochemically processed ZnTe for application in photo detection and sensor related functions.

We report vertical contact light-emitting diodes (VCLEDs), that are based on heterojunctions formed by using the point contacts of n-ZnO nanorods (NRs) to the p-type semiconductor substrate and that are fabricated using a new approach to the formation of LEDs (Appl. Phys. Lett. 98, 093110 (2011)). A p-type GaN film grown on a sapphire substrate was used to form n-ZnO NRs/p-GaN VCLEDs on a large area of about 4 cm2. The VCLEDs emitted a pure blue electroluminescence with high efficiency. Electroluminescence at 470 nm, which is visible to the naked eye, started at small current of about 50 μA and is attributed to the good optical properties of the structurallyperfect heterojunctions in the point contacts. The VCLED configuration allows the creation of ZnO/p-GaN nano-LEDs of high density and high-quality with a greatly reduced concentration of nonradiative defects in the active regions. The VCLEDs showed the high brightness of light required for active matrix displays and general solid-state lighting.

We studied the optical, electrical and magnetic properties of ZnO films prepared by using a pulsed laser deposition method. Low-temperature photoluminescence (PL) measurements revealed a strong emission line at 3.333 eV. A dependence of this emission intensity on oxygen adsorbed on the surface was observed, indicating a near-surface origin for the emission. The transition at 3.333 eV was attributed to bound exciton, and the observed anomalously small thermal activation energy in comparison with the localization energy could be explained by a modification of the surface state. The observed resistance switching effect and ferromagnetism in the ZnO films were related to the existence of defects responsible for the PL emission at 3.333 eV.

GaN epilayers on AlN buffer layers with various thicknesses were grown on sapphire substrates by using plasma-assisted molecular-beam epitaxy. The GaN epilayer with an AlN buffer layer was much smaller than the GaN epilayer without an AlN buffer layer. The crystal quality of the GaN active layer was improved by utilizing an AlN layer, which acted as a nucleation layer. The reduced defect density promoted GaN coalition. The double-crystal rocking curves and the photoluminescence spectra showed that the GaN epilayer grown on a 4-nm AlN buffer layer had the best quality among the several kinds of samples. The photoluminescence intensity of the GaN epilayer which is related to the density of the crystal defects was lower when an AlN buffer layer was used the thin AlN nucleation layer protected against stain propagation. These results indicate that GaN epilayers grown on AIN buffer layers hold promise for applications in short-wavelength optoelectronic devices.

This study aims at evaluating nonlinear hydrodynamic pressures on the inner wall of rigid cylindrical tanks, resulting from liquid sloshing due to the simultaneous action of two horizontal and one vertical ground motion components. For this purpose, the computational model that can predict realistic dynamic fluid responses is validated through comparison of simulated and experimental results reported in the literature. Using the validated computational fluid dynamics modeling technique, the computational model of a prototype cylindrical steel water tank constructed in California is developed to examine the effect of vertical ground motion component on the hydrodynamic pressure response of the tank. Comparison with and without vertical excitation indicates that the vertical motion significantly increases the hydrodynamic pressure on the inner wall of the tanks. Additionally, the effect of water elevation and tank dimensions (height and diameter) on the hydrodynamic pressure is investigated when the tanks are simultaneously subjected to two horizontal and one vertical ground motion components. As the water level and tank dimensions increase, the peak hydrodynamic pressure increases due to the increase of liquid mass.

Tin sulfides are promising materials in the fields of photoelectronics and photovoltaics because of their appropriate energy bands. However, doping in SnS2 can improve the stability and robustness of this material in potential applications. Herein, we report the synthesis of SnS2 nanoflakes with Zn doping via simple hydrothermal route. The effect of doping Zn was found to display a huge influence in the structural and crystalline order of as synthesized SnS2. Their optical properties attest Zn doping of SnS2 results in reduction of the band gap which benefits strong visible-light absorption. Significantly, enhanced photoresponse was observed with respect to pristine SnS2. Such enhancement could result in improved electronic conductivity and sensitivity due to Zn doping at appropriate concentration. These excellent performances show that Sn1&minus, xZnxS2 nanoflakes could offer huge potential for nanoelectronics and optoelectronics device applications.

Vertically aligned and uniform ZnO1−xSx NRs with blue–green luminescence were obtained on glass using the hydrothermal method. The ratio of the blue to green luminescence intensities increases with thiourea doping and the positions of the luminescence peaks are red-shifted. At high doping concentration of thiourea, phase and morphology separations lead to formation of NR arrays with varied luminescent and electronic properties. The vertical ZnOS NRs p–n junctions could be self-assembled as indicated by SEM measurements in a through-the lens secondary electron mode.

In this work, the successful synthesis of ZnSe nanowires using alumina template by simple and facile electroless template technique has been reported. Morphological characterization of the synthesized nanowires has been done by X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. The optical characterizations were conducted by UV–visible and time resolved photo-luminescence. Grain size of synthesized ZnSe nanowires was also calculated using the XRD results. The calculated crystallite size was found to be 6.80 nm. SEM analysis confirms the fabrication of nanowires successfully and it also confirms the size of the nanowires as per the template parameters. The calculated band gap value of 3.03 eV shows the origin of quantum confinement effect in ZnSe nanowires even at the 100 nm scale. The time resolved photoluminescence result indicates that the ZnSe nanowires can be a promising material for luminescent applications in micro-second time domain.

Mi Sun Lee, Min Cheol Kim, Chan Hee Lee, Hoey Kyung Park, Tae Won Kang, Hae Seong Jeong*,Kyoung Ah Han*, Weon Hoe Huh* and Ji Cheol You*Department Chemical Engineering, Kongju National University, 275 Budae-dong, Cheonan, Chungnam 330-717, Korea *Silice Co., Ltd., Korea Institute of Industrial Technology PP2-303,35-3, Ipjang-myeon, Seobuk-gu, Cheonan, Chungnam 331-822, Korea(Received 8 March 2013; accepted 31 March 2013)

Micro-fabricated single-layer graphenes (SLGs) on a silicon dioxide (SiO2)/Si substrate, a silicon nitride (SiN) membrane, and a suspended architecture are presented for their use as temperature sensors. These graphene temperature sensors act as resistance temperature detectors, showing a quadratic dependence of resistance on the temperature in a range between 283 K and 303 K. The observed resistance change of the graphene temperature sensors are explained by the temperature dependent electron mobility relationship (~T−4) and electron-phonon scattering. By analyzing the transient response of the SLG temperature sensors on different substrates, it is found that the graphene sensor on the SiN membrane shows the highest sensitivity due to low thermal mass, while the sensor on SiO2/Si reveals the lowest one. Also, the graphene on the SiN membrane reveals not only the fastest response, but also better mechanical stability compared to the suspended graphene sensor. Therefore, the presented results show that the temperature sensors based on SLG with an extremely low thermal mass can be used in various applications requiring high sensitivity and fast operation.

Scientific Reports 6: Article number: 31224; published online: 05 August 2016; updated: 14 November 2016

A MoS2 nanosphere memristor with lateral gold electrodes was found to show photoresistive switching. The new device can be controlled by the polarization of nanospheres, which causes resistance switching in an electric field in the dark or under white light illumination. The polarization charge allows to change the switching voltage of the photomemristor, providing its multi-level operation. The device, polarized at a voltage 6 V, switches abruptly from a high resistance state (HRSL6) to a low resistance state (LRSL6) with the On/Off resistance ratio of about 10 under white light and smooth in the dark. Analysis of device conductivity in different resistive states indicates that its resistive state could be changed by the modulation of the charge in an electric field in the dark or under light, resulting in the formation/disruption of filaments with high conductivity. A MoS2 photomemristor has great potential as a multifunctional device designed by using cost-effective fabrication techniques.

We present an investigation of free-carrier screening in coupled asymmetric GaN quantum discs with embedded AlGaN barriers using time-integrated and time-resolved microphotoluminescence measurements, supported by three-dimensional multiband k∙p computational modeling. We observe that with increasing optical excitation the carrier lifetime decreases and emission energy blueshifts. This originates from the screening of built-in piezo- and pyroelectric fields in the quantum discs by photogenerated free carriers. Due to nonresonant tunneling of carriers from the smaller disk to the larger disk, free-carrier screening is enhanced in the larger disk. Computational modeling was in good agreement with the experimental results.

Massive Open Online Course(MOOC) is recently being spread worldwide around the U.S.A, and contrary to existing online lectures, it is a type of lecture allowing the communication between the instructor and each student. With the expansion of MOCC system use, this study aimed to investigate what factors make the people needing to be educated use a MOOC. For this aim, this study set a research model which on the basis of TAM(Technology Acceptance Mechanism) and empirically analyzed the model and identified the relationships among influential factors.

The growth of hexagonal wurzite one dimensional (1D) gallium nitride (GaN) nanostructures on sapphire substrates using hydride vapor phase epitaxy (HVPE) process was carried out at two different temperatures (973 K and 1023 K). The GaN nanoneedles were formed at 973 K and hexagonal nanorods get formed at 1023 K. The morphologies of these nanostructures were studied using high resolution scanning electron microscope. X-ray diffraction and micro-Raman spectroscopy measurements confirmed that the as grown GaN nanostructures are of hexagonal wurtzite structure without any oxide phase. The emission properties of these nanostructures have been investigated using photoluminescence.

We have investigated the doping transition of one-dimensional (1-D) doped-ZnO nanorods with Kelvin probe force microscopy (KPFM). Vertically aligned (undoped, As-doped, and undoped/As-doped homo-junction) ZnO nanorods were grown on Si (111) substrates without any catalyst by vapor phase transport. Individual ZnO nanorods are removed from the substrates and transferred onto thin Au films grown on Si substrates. The morphology and surface potentials of the nanorods were measured simultaneously by the KPFM. For the homo-junction nanorods with ~ 250 nm in diameter, the KPFM image shows localization of the doping transition along the nanorods. The measured Kelvin signal (surface potential) across the junction induces the work function difference between the undoped and the As-doped region of ~ 85 meV. Also, the work function of As-doped nanorods is ~ 95 meV higher than that of intrinsically undoped nanorods grown in similar conditions. These consistent results indicate that the KPFM is reliable to determine the localization of the doping transition in 1-D structures.

In this study, we demonstrate the electronic properties of As-doped homojunction ZnO nanorods by Kelvin probe force microscopy (KPFM). The self-assembled undoped/As-doped homojunction ZnO nanorods were grown on Si (111) substrates by using vapor phase transport. Individual nanorods were transferred onto Au films grown on Si substrates. The morphology and surface potentials of the ZnO nanorods were simultaneously measured by KPFM. For the homojunction nanorods with ~200 nm in diameter, the KPFM images show obviously doping transition across the junction region, indicating local doping types. Also, the surface potential difference across the junction was measured to be ~85 mV, which could be the result from the work function difference between undoped and As-doped region. It is in good agreement with the work function difference of ~95 meV between the As-doped p-type and intrinsic n-type nanorods in the same measurement condition. The work function of the doped ZnO nanorods measured by KPFM is discussed in terms of surface band bending induced by surface states of ZnO. Copyright © 2011 John Wiley & Sons, Ltd.

Curved structural members are widely seen in our surroundings, such as railway supports in playgrounds resembling a c-ring structure. The common geometry of the curved member consists of a segment of a circular ring with a uniform width. The curved section is of constant width in most cardiovascular stents. This study focuses on curved strut members whose width changes along the curved segment. The location of the maximum equivalent stress varies depending on the manner in which the width changes. When the width is constant or larger toward the top, the maximum equivalent stress is developed at the top. Meanwhile, when the area is reduced toward the bottom, the largest equivalent stress is developed some distance from the top. Simple equations, based on the mechanics of materials and the theory of elasticity, were compared favorably with the results from finite element analysis. Included are elaborations of the distribution of the change of stress. The suggested strategy of changing the width, with refinements, could be applied to the optimal design of structural members, including pipes and medical devices such as stents.

Scanning electron microscopy and transmission electron microscopy images and selected area electron diffraction pattern showed that the one-dimensional GaN nanorods with [0001]-oriented single-crystalline wurzite structures were formed on Si (111) substrates by using hydride vapor-phase epitaxy without a catalyst. Although some stacking faults and inversion domain boundaries existed in the GaN nanorods, few other defects such as threading dislocations were observed. The formation of the facet plane in the N-polar region of the GaN nanorod containing an inversion domain boundary originated from the slow growth rate, followed by the lateral adatom diffusion from the Ga-polar region to reduce the length difference.

The effects of washing and heat treatment on photoluminescence (PL) behavior from artificial opals are studied. The PL spectra excited by N2-laser radiation (337 nm) display a broad maximum at around 435 nm and range from ∼340 to ∼700 nm. It is found that washing of the opal in different solvents and liquids leads to suppression of the long wavelength PL band at ∼500 nm, whereas heat treatment in air and vacuum results in a decrease in intensity of both of the PL bands. The obtained results indicate that the emission centers located on the surface of SiO2 spheres constructing artificial opal may be responsible for the PL band around ∼500 nm.

Capacitance-voltage (C-V) and Deep-level transient spectroscopy (DLTS) measurements on AlxGa1-xN/GaN heterostructures were performed to investigate the existence of the carriers and the behavior of the deep levels in the AlxGa1-xN/GaN heterointerface. The C-V depth profile showed that the carrier concentration existed at the AlxGa1-xN/GaN heterointerface was 4 × 1012 cm2. The DLTS results showed two deep levels. The capture cross-section of the deep level related to the two-dimensional electron gas decreased with increasing depth, resulting from the existence of the different deep levels in each region.

The high-resolution scanning electron microscopy (HRSEM) image showed that selfassembled ZnSe small quantum dots (QDs) and large nanodots with a pyramid shape were formed in the Cl-doped ZnSe epilayers grown on GaAs (100) substrates. The formation of the ZnSe QDs was attributed to three-dimensional growth controlled by distribution of the impurities in the Cldoped ZnSe epilayrs. Cathodoluminescence (CL) measurements at room temperature revealed the emission peak at 3.1 eV corresponding to the blue shift approximately 400 meV from the near band edge emission of 2.7 eV in the bulk ZnSe. The blue shifted CL peak indicates the quantum confinement effect resulting from the formation of the ZnSe QDs in the Cl-doped ZnSe thin film. While the peak position of the donor-acceptor pair emission shifted to higher energies with decreasing temperature, the band-edge emission peak for the QDs did not significantly change.

Gallium nitride (GaN) nanorods were grown on Al 2 O 3 (0 0 0 1) substrates at 500 °C by hydride vapor phase epitaxy (HVPE) and their structural and optical properties were improved by e-beam annealing. After e-beam annealing for 4 h by applying an acceleration energy of 30 keV, cathodoluminescence peak positions for the single nanorod and the grouped nanorods were shifted toward lower energy region by 46 and 34 meV, respectively. For Raman scattering spectroscopy measurements, it was also observed that E 2 (high) peak positions shifted to the lower frequency region. Using the deviation between E 2 (high) peak positions for before and after e-beam annealing, the relaxation of biaxial compressive stress was calculated to be ∼0.8 Gpa. These results suggest that the optical and structural properties of GaN nanorods could be improved by e-beam annealing.

The optical properties and the deep levels in bulk Si 1− x Mn x formed by using an implantation and annealing method were investigated. Transmission electron microscopy, X-ray diffraction, and Hall-effect measurements showed that the annealed bulk Si 1− x Mn x samples were p-type crystalline semiconductors. The photoluminescence spectra for the annealed bulk Si 1− x Mn x material showed luminescence peaks corresponding to excitons bound to neutral acceptors and related to dislocations due to the existence of Mn impurities. Deep-level transient spectroscopy results for the annealed bulk Si 1− x Mn x showed deep levels related to the interstitial and substitutial sites of the Mn + ions. These results can help improve understanding of the optical properties and the deep levels in annealed bulk Si 1− x Mn x material.