Showing papers on "Substrate (electronics) published in 2014"

Germanene: a novel two-dimensional germanium allotrope akin to graphene and silicene

Abstract: We have grown an atom-thin, ordered, two-dimensional multi-phase film in situ through germanium molecular beam epitaxy using a gold (111) surface as a substrate. Its growth is similar to the formation of silicene layers on silver (111) templates. One of the phases, forming large domains, as observed in scanning tunneling microscopy, shows a clear, nearly flat, honeycomb structure. Thanks to thorough synchrotron radiation core-level spectroscopy measurements and advanced density functional theory calculations we can identify it as a ?3????3 R(30?) germanene layer in conjunction with a ?7????7 R(19.1?) Au(111) supercell, presenting compelling evidence of the synthesis of the germanium-based cousin of graphene on gold.

Wafer-Scale Growth of Single-Crystal Monolayer Graphene on Reusable Hydrogen-Terminated Germanium

Abstract: The uniform growth of single-crystal graphene over wafer-scale areas remains a challenge in the commercial-level manufacturability of various electronic, photonic, mechanical, and other devices based on graphene. Here, we describe wafer-scale growth of wrinkle-free single-crystal monolayer graphene on silicon wafer using a hydrogen-terminated germanium buffer layer. The anisotropic twofold symmetry of the germanium (110) surface allowed unidirectional alignment of multiple seeds, which were merged to uniform single-crystal graphene with predefined orientation. Furthermore, the weak interaction between graphene and underlying hydrogen-terminated germanium surface enabled the facile etch-free dry transfer of graphene and the recycling of the germanium substrate for continual graphene growth.

High-Performance Flexible Broadband Photodetector Based on Organolead Halide Perovskite

Abstract: Organolead halide perovskites have attracted extensive attentions as light harvesting materials for solar cells recently, because of its high charge-carrier mobilities, high photoconversion efficiencies, low energy cost, ease of deposition, and so on. Herein, with CH3NH3PbI3 film deposited on flexible ITO coated substrate, the first organolead halide perovskite based broadband photodetector is demonstrated. The organolead halide perovskite photodetector is sensitive to a broadband wavelength from the ultraviolet light to entire visible light, showing a photo-responsivity of 3.49 A W−1, 0.0367 A W−1, an external quantum efficiency of 1.19×103%, 5.84% at 365 nm and 780 nm with a voltage bias of 3 V, respectively. Additionally, the as-fabricated photodetector exhibit excellent flexibility and robustness with no obvious variation of photocurrent after bending for several times. The organolead halide perovskite photodetector with high sensitivity, high speed and broad spectrum photoresponse is promising for further practical applications. And this platform creates new opportunities for the development of low-cost, solution-processed and high-efficiency photodetectors.

Shape Evolution of Monolayer MoS2 Crystals Grown by Chemical Vapor Deposition

Abstract: Atmospheric-pressure chemical vapor deposition (CVD) is used to grow monolayer MoS2 two-dimensional crystals at elevated temperatures on silicon substrates with a 300 nm oxide layer. Our CVD reaction is hydrogen free, with the sulfur precursor placed in a furnace separate from the MoO3 precursor to individually control their heating profiles and provide greater flexibility in the growth recipe. We intentionally establish a sharp gradient of MoO3 precursor concentration on the growth substrate to explore its sensitivity to the resultant MoS2 domain growth within a relatively uniform temperature range. We find that the shape of MoS2 domains is highly dependent upon the spatial location on the silicon substrate, with variation from triangular to hexagonal geometries. The shape change of domains is attributed to local changes in the Mo:S ratio of precursors (1:>2, 1:2, and 1:<2) and its influence on the kinetic growth dynamics of edges. These results improve our understanding of the factors that influence the...

Shape Evolution of Monolayer MoS 2 Crystals Grown by Chemical Vapor Deposition

Abstract: Atmospheric-pressure chemical vapor deposi- tion (CVD) is used to grow monolayer MoS2 two-dimensional crystals at elevated temperatures on silicon substrates with a 300 nm oxide layer. Our CVD reaction is hydrogen free, with the sulfur precursor placed in a furnace separate from the MoO3 precursor to individually control their heating profiles and provide greater flexibility in the growth recipe. We intentionally establish a sharp gradient of MoO3 precursor concentration on the growth substrate to explore its sensitivity to the resultant MoS2 domain growth within a relatively uniform temperature range. We find that the shape of MoS2 domains is highly dependent upon the spatial location on the silicon substrate, with variation from triangular to hexagonal geometries. The shape change of domains is attributed to local changes in the Mo:S ratio of precursors (1:>2, 1:2, and 1:<2) and its influence on the kinetic growth dynamics of edges. These results improve our understanding of the factors that influence the growth of MoS2 domains and their shape evolution.

Enhanced Third-Harmonic Generation in Silicon Nanoparticles Driven by Magnetic Response

Abstract: We observe enhanced third-harmonic generation from silicon nanodisks exhibiting both electric and magnetic dipolar resonances. Experimental characterization of the nonlinear optical response through third-harmonic microscopy and spectroscopy reveals that the third-harmonic generation is significantly enhanced in the vicinity of the magnetic dipole resonances. The field localization at the magnetic resonance results in two orders of magnitude enhancement of the harmonic intensity with respect to unstructured bulk silicon with the conversion efficiency limited only by the two-photon absorption in the substrate.

The effect of the substrate on the Raman and photoluminescence emission of single-layer MoS2

Abstract: We quantitatively study the Raman and photoluminescence (PL) emission from single-layer molybdenum disulfide (MoS2) on dielectric (SiO2, hexagonal boron nitride, mica and the polymeric dielectric Gel-Film®) and conducting substrates (Au and few-layer graphene). We find that the substrate can affect the Raman and PL emission in a twofold manner. First, the absorption and emission intensities are strongly modulated by the constructive/destructive interference within the different substrates. Second, the position of the A1g Raman mode peak and the spectral weight between neutral and charged excitons in the PL spectra are modified by the substrate. We attribute this effect to substrate-induced changes in the doping level and in the decay rates of the excitonic transitions. Our results provide a method to quantitatively study the Raman and PL emission from MoS2-based vertical heterostructures and represent the first step in ad hoc tuning the PL emission of 1L MoS2 by selecting the proper substrate.

Laser printing of silicon nanoparticles with resonant optical electric and magnetic responses

Abstract: Silicon nanoparticles are of interest for their optical properties, for example, in light scattering. Here, Zywietz et al. achieve the laser printing of silicon nanoparticles on a substrate at predefined positions, and with control over their crystalline phase.

Direct Writing of Gallium‐Indium Alloy for Stretchable Electronics

Abstract: In this paper, a direct writing method for gallium-indium alloys is presented. The relationships between nozzle inner diameter, standoff distance, flow rate, and the resulting trace geometry are demonstrated. The interaction between the gallium oxide layer and the substrate is critically important in understanding the printing behavior of the liquid metal. The difference between receding and advancing contact angles demonstrates that the adhesion of the oxide layer to the substrate surface is stronger than the wetting of the surface by the gallium-indium alloy. This further demonstrates why free-standing structures such as the traces described herein can be realized. In addition to the basic characterization of the direct writing process, a design algorithm that is generalizable to a range of trace geometries is developed. This method is applied to the fabrication of an elastomer-encapsulated strain gauge that displays an approximately linear behavior through 50% strain with a gauge factor of 1.5.

All Two-Dimensional, Flexible, Transparent, and Thinnest Thin Film Transistor

Abstract: In this article, we report only 10 atomic layer thick, high mobility, transparent thin film transistors (TFTs) with ambipolar device characteristics fabricated on both a conventional silicon platform as well as on a flexible substrate. Monolayer graphene was used as metal electrodes, 3–4 atomic layers of h-BN were used as the gate dielectric, and finally bilayers of WSe2 were used as the semiconducting channel material for the TFTs. The field effect carrier mobility was extracted to be 45 cm2/(V s), which exceeds the mobility values of state of the art amorphous silicon based TFTs by ∼100 times. The active device stack of WSe2–hBN–graphene was found to be more than 88% transparent over the entire visible spectrum and the device characteristics were unaltered for in-plane mechanical strain of up to 2%. The device demonstrated remarkable temperature stability over 77–400 K. Low contact resistance value of 1.4 kΩ-μm, subthreshold slope of 90 mv/decade, current ON–OFF ratio of 107, and presence of both electr...

Ultrastable gold substrates for electron cryomicroscopy

Abstract: Despite recent advances, the structures of many proteins cannot be determined by electron cryomicroscopy because the individual proteins move during irradiation. This blurs the images so that they cannot be aligned with each other to calculate a three-dimensional density. Much of this movement stems from instabilities in the carbon substrates used to support frozen samples in the microscope. Here we demonstrate a gold specimen support that nearly eliminates substrate motion during irradiation. This increases the subnanometer image contrast such that α helices of individual proteins are resolved. With this improvement, we determine the structure of apoferritin, a smooth octahedral shell of α-helical subunits that is particularly difficult to solve by electron microscopy. This advance in substrate design will enable the solution of currently intractable protein structures.

Physically Flexible, Rapid‐Response Gas Sensor Based on Colloidal Quantum Dot Solids

Abstract: A gas sensor based on PbS colloidal quantum dots (CQDs) is constructed on a paper substrate, yielding flexible, rapid-response NO₂ gas sensors, fabricated from the solution phase. The devices are highly sensitive and fully recoverable at room temperature, which is attributed to the excellent access of gas molecules to the CQD surface, realized by surface ligand removal, combined with the desirable binding energy of NO₂ with the PbS CQDs.

Stretchable all-solid-state supercapacitor with wavy shaped polyaniline/graphene electrode

Abstract: A stretchable electronic device can retain its functionalities during high-level mechanical deformation, and stimulates the applications in the field of wearable and bio-implantable electronics. Efficient energy storage devices are an indispensable component in stretchable electronic systems. To integrate power supplies together with electronic devices that are mechanically flexible and stretchable, we demonstrate a new kind of stretchable all-solid-state supercapacitor, which consists of two slightly separated polyaniline/graphene electrodes in a wavy shape, with a phosphoric acid/polyvinyl alcohol gel as the solid-state electrolyte and separator. The as-fabricated wavy shaped supercapacitor was encapsulated in an elastomeric substrate which can be stretched to a large extent without mechanical degradation. The supercapacitor exhibited a maximum specific capacitance of 261 F g−1. Electrochemical cycling testing with the supercapacitor showed 89% capacitance retention over 1000 charge–discharge cycles at a current density of 1 mA cm−2. The bending and stretching tests showed that the supercapacitor maintained high mechanical strength and high capacitance simultaneously, even under a strain of 30%. This stretchable all-solid-state supercapacitor shows great potential as an energy storage device for stretchable electronic systems.

Finfet devices with unique fin shape and the fabrication thereof

Abstract: A semiconductor device includes a PMOS FinFET and an NMOS FinFET. The PMOS FinFET includes a substrate, a silicon germanium layer disposed over the substrate, a silicon layer disposed over the silicon germanium layer, and a PMOS fin disposed over the silicon layer. The PMOS fin contains silicon germanium. The NMOS FinFET includes the substrate, a silicon germanium oxide layer disposed over the substrate, a silicon oxide layer disposed over the silicon germanium oxide layer, and an NMOS fin disposed over the silicon oxide layer. The NMOS fin contains silicon. The silicon germanium oxide layer and the silicon oxide layer collectively define a concave recess in a horizontal direction. The concave recess is partially disposed below the NMOS fin.

Organic Thin Film Transistors: Structures, Models, Materials, Fabrication, and Applications: A Review

Abstract: Organic thin film transistor (OTFT) based device modeling and circuit application is a rapidly emerging research area. Taking cognizance of this fact, our paper reviews various basic to advanced OTFT structures, their performance parameters, materials of individual OTFT layers, their molecular structures, OTFT charge transport phenomena, and fabrication techniques. The performance of p- and n-type conducting polymer and small molecule organic semiconductors are reviewed primarily in terms of field effect mobility, current on/off ratio, and operating voltage for various OTFT structures. Moreover, different organic/inorganic materials for realizing the dielectric layer, electrodes, and the substrate in an OTFT are analyzed. Some of the compact models that are essential for predicting and optimizing the device performance are described that takes into account the mobility enhancement factor and channel length modulation. A detailed study of the single gate, dual gate, vertical channel, and cylindrical gate O...

Ideal Three-Dimensional Electrode Structures for Electrochemical Energy Storage

Abstract: Three-dimensional electrodes offer great advantages, such as enhanced ion and electron transport, increased material loading per unit substrate area, and improved mechanical stability upon repeated charge-discharge. The origin of these advantages is discussed and the criteria for ideal 3D electrode structure are outlined. One of the common features of ideal 3D electrodes is the use of a 3D carbon- or metal-based porous framework as the structural backbone and current collector. The synthesis methods of these 3D frameworks and their composites with redox-active materials are summarized, including transition metal oxides and conducting polymers. The structural characteristics and electrochemical performances are also reviewed. Synthesis of composite 3D electrodes is divided into two types - template-assisted and template-free methods - depending on whether a pre-made template is required. The advantages and drawbacks of both strategies are discussed.

Plasmoelectric potentials in metal nanostructures

Abstract: The conversion of optical power to an electric potential is of general interest for energy applications and is typically obtained via optical excitation of semiconductor materials. We developed a method for achieving electric potential that uses an all-metal geometry based on the plasmon resonance in metal nanostructures. In arrays of gold nanoparticles on an indium tin oxide substrate and arrays of 100-nanometer-diameter holes in 20-nanometer-thick gold films on a glass substrate, we detected negative and positive surface potentials during monochromatic irradiation at wavelengths below or above the plasmon resonance, respectively. We observed plasmoelectric surface potentials as large as 100 millivolts under illumination of 100 milliwatts per square centimeter. Plasmoelectric devices may enable the development of all-metal optoelectronic devices that can convert light into electrical energy.

Integrated germanium optical interconnects on silicon substrates

Abstract: The integration of germanium quantum-well devices and low-loss waveguides with silicon substrates shows promise for realizing low-loss, on-chip photonic interconnects.

Large-Area Monolayer Hexagonal Boron Nitride on Pt Foil

Abstract: Hexagonal boron nitride (h-BN) has recently been in the spotlight due to its numerous applications including its being an ideal substrate for two-dimensional electronics, a tunneling material for vertical tunneling devices, and a growth template for heterostructures. However, to obtain a large area of h-BN film while maintaining uniform thickness is still challenging and has not been realized. Here, we report the systematical study of h-BN growth on Pt foil by using low pressure chemical vapor deposition with a borazine source. The monolayer h-BN film was obtained over the whole Pt foil (2 × 5 cm2) under <100 mTorr, where the size is limited only by the Pt foil size. A borazine source was catalytically decomposed on the Pt surface, leading to the self-limiting growth of the monolayer without the associating precipitation, which is very similar to the growth of graphene on Cu. The orientation of the h-BN domains was largely confined by the Pt domain, which is confirmed by polarizing optical microscopy (POM...

Methods for forming doped silicon oxide thin films

Abstract: The present disclosure relates to the deposition of dopant films, such as doped silicon oxide films, by atomic layer deposition processes. In some embodiments, a substrate in a reaction space is contacted with pulses of a silicon precursor and a dopant precursor, such that the silicon precursor and dopant precursor adsorb on the substrate surface. Oxygen plasma is used to convert the adsorbed silicon precursor and dopant precursor to doped silicon oxide.

Different shades of oxide: from nanoscale wetting mechanisms to contact printing of gallium-based liquid metals.

Abstract: Gallium-based liquid metals are of interest for a variety of applications including flexible electronics, soft robotics, and biomedical devices. Still, nano- to microscale device fabrication with these materials is challenging because, despite having surface tension 10 times higher than water, they strongly adhere to a majority of substrates. This unusually high adhesion is attributed to the formation of a thin oxide shell; however, its role in the adhesion process has not yet been established. In this work, we demonstrate that, dependent on dynamics of formation and resulting morphology of the liquid metal–substrate interface, GaInSn adhesion can occur in two modes. The first mode occurs when the oxide shell is not ruptured as it makes contact with the substrate. Because of the nanoscale topology of the oxide surface, this mode results in minimal adhesion between the liquid metal and most solids, regardless of substrate’s surface energy or texture. In the second mode, the formation of the GaInSn–substrat...

Highly flexible, all solid-state micro-supercapacitors from vertically aligned carbon nanotubes

Abstract: We report a highly flexible planar micro-supercapacitor with interdigitated finger electrodes of vertically aligned carbon nanotubes (VACNTs). The planar electrode structures are patterned on a thin polycarbonate substrate with a facile, maskless laser-assisted dry transfer method. Sputtered Ni is used to reduce the in-plane resistance of the VACNT electrodes. An ionogel, an ionic liquid in a semi-solid matrix, is used as an electrolyte to form a fully solid-state device. We measure a specific capacitance of 430 μF cm−2 for a scan rate of 0.1 V s−1 and achieve rectangular cyclic voltammograms at high scan rates of up to 100 V s−1. Minimal change in capacitance is observed under bending. Mechanical fatigue tests with more than 1000 cycles confirm the high flexibility and durability of the novel material combination chosen for this device. Our results indicate that this scalable and facile fabrication technique shows promise for application in integrated energy storage for all solid-state flexible microdevices.

Electrochemical Characterization of TiO2 Blocking Layers for Dye-Sensitized Solar Cells

Abstract: Thin compact layers of TiO2 are grown by thermal oxidation of Ti, by spray pyrolysis, by electrochemical deposition, and by atomic layer deposition. These layers are used in dye-sensitized solar cells to prevent recombination of electrons from the substrate (FTO or Ti) with the hole-conducting medium at this interface. The quality of blocking is evaluated electrochemically by methylviologen, ferro/ferricyanide, and spiro-OMeTAD as the model redox probes. Two types of pinholes in the blocking layers are classified, and their effective area is quantified. Frequency-independent Mott–Schottky plots are fitted from electrochemical impedance spectroscopy. Certain films of the thicknesses of several nanometers allow distinguishing the depletion layer formation both in the TiO2 film and in the FTO substrate underneath the titania film. The excellent blocking function of thermally oxidized Ti, electrodeposited film (60 nm), and atomic-layer-deposited films (>6 nm) is documented by the relative pinhole area of less...

Dual-band micro strip antenna based on split resonance ring

Abstract: The utility model discloses a dual-band micro strip antenna based on a split resonance ring and belongs to the technical field of the antenna. The antenna comprise a radiation portion, a medium substrate, a grounding board and a feed wire, wherein the radiation portion is arranged on the medium substrate and comprises the metal split resonance ring and a metal radiation paster, the metal split resonance ring surrounds the metal radiation paster without contact, a center of the metal radiation paster is arranged on a symmetric line of the metal split resonance ring and is not on a circle center, the grounding board and the medium substrate are parallelly arranged below the metal radiation paster with intervals, the feed wire comprises an inner core wire and a shielding layer, and the inner core wire exposed at an upper end of the feed wire penetrates through the grounding board and the medium substrate to connect with the metal radiation paster. The dual-band micro strip antenna based on the split resonance ring has advantages of relatively high radiation efficiency and gain, simple and compact structure and low production cost.

Silicon Photonic Integration Platform—Have We Found the Sweet Spot?

Abstract: The current trend in silicon photonics towards higher levels of integration as well as the model of using CMOS foundries for fabrication are leading to a need for standardization of substrate parameters and fabrication processes In particular, for several established research and development foundries that grant general access, silicon-on-insulator wafers with a silicon thickness of 220 nm have become the standard substrate for which devices and circuits have to be designed In this study we investigate the role of silicon device layer thickness in design optimization of various components that need to be integrated in a typical optical transceiver, including both passive ones for routing, wavelength selection, and light coupling as well as active ones such as monolithic modulators and on-chip lasers produced by hybrid integration We find that in all devices considered there is an advantage in using a silicon thickness larger than 220 nm, either for improved performance or for simplified fabrication processes and relaxed tolerances

Selective atomic layer deposition of zirconia on copper patterned silicon substrates using ethanol as oxygen source as well as copper reductant

Abstract: The authors report a new chemical approach for the selective atomic layer deposition of ultrathin layers of zirconium oxide (ZrO2) on copper patterned silicon surfaces. Instead of using common atomic layer deposition (ALD) oxygen sources such as water, oxygen, or ozone, the authors use ethanol, which serves as oxygen source for the ALD on the silicon side and as effective reducing agent on the copper side, thereby selectively depositing ZrO2 film on the silicon surface of the substrate without any deposition on copper up to at least 70 ALD cycles. The resulting ZrO2 nanofilm is found to be an effective copper diffusion barrier at temperatures at least up to 700 °C.

Mobility improvement and temperature dependence in MoSe2 field-effect transistors on parylene-C substrate

Abstract: We report low-temperature scanning tunneling microscopy characterization of MoSe2 crystals and the fabrication and electrical characterization of MoSe2 field-effect transistors on both SiO2 and parylene-C substrates. We find that the multilayer MoSe2 devices on parylene-C show a room-temperature mobility close to the mobility of bulk MoSe2 (100–160 cm2 V–1 s–1), which is significantly higher than that on SiO2 substrates (≈50 cm2 V–1 s–1). The room-temperature mobility on both types of substrates are nearly thickness-independent. Our variable-temperature transport measurements reveal a metal–insulator transition at a characteristic conductivity of e2/h. The mobility of MoSe2 devices extracted from the metallic region on both SiO2 and parylene-C increases up to ≈500 cm2 V–1 s–1 as the temperature decreases to ≈100 K, with the mobility of MoSe2 on SiO2 increasing more rapidly. In spite of the notable variation of charged impurities as indicated by the strongly sample-dependent low-temperature mobility, the m...

Pulsed laser-deposited MoS₂ thin films on W and Si: field emission and photoresponse studies.

Abstract: We report field electron emission investigations on pulsed laser-deposited molybdenum disulfide (MoS2) thin films on W-tip and Si substrates. In both cases, under the chosen growth conditions, the dry process of pulsed laser deposition (PLD) is seen to render a dense nanostructured morphology of MoS2, which is important for local electric field enhancement in field emission application. In the case of the MoS2 film on silicon (Si), the turn-on field required to draw an emission current density of 10 μA/cm2 is found to be 2.8 V/μm. Interestingly, the MoS2 film on a tungsten (W) tip emitter delivers a large emission current density of ∼30 mA/cm2 at a relatively lower applied voltage of ∼3.8 kV. Thus, the PLD-MoS2 can be utilized for various field emission-based applications. We also report our results of photodiode-like behavior in (n- and p- type) Si/PLD-MoS2 heterostructures. Finally we show that MoS2 films deposited on flexible kapton substrate show a good photoresponse and recovery. Our investigations t...