Showing papers presented at "International Conference on Nanotechnology in 2020"

Effects of Spacer and Single-Charge Trap on Voltage Transfer Characteristics of Gate-All-Around Silicon Nanowire CMOS Devices and Circuits

Abstract: We report the effects of the spacer and the single-charge trap (SCT) on the voltage transfer characteristics of cylindrical-shape gate-all-around (GAA) silicon (Si) nanowire (NW) metal-oxide-semiconductor field effect transistor (MOSFETs). We explore the impact of low-x spacer, high-x spacer, and dual spacer (DS) on electrical characteristics of the GAA Si NW MOSFET with a gate length of 10 nm. Compared with the nominal device (i.e., the device without spacer), the device with DS possesses 68.8% reduction on the normalized off-current and 29.4% increase on the normalized on-current for n- and p-type devices. Similarly, 21.1% and 3.38% improvements on the normalized high and low noise margins can be achieved for the GAA Si NW complementary metal-oxide-semiconductor (CMOS) circuit. Notably, the voltage transfer characteristics induced by the acceptor- and donor-type SCT for the CMOS circuit with DS possesses 2.64% and 3.82% enhancements for the normalized high and low noise margins compared with the nominal one.

Temperature investigation of a Novel 3nm TF-Bulk FinFET for Improved Performance

Abstract: In this investigation, a novel Truncated Fin (TF) Junctionless (JL) bulk FinFET is compared over it's conventional structure. This paper is the analysis of highperformance temperature characteristics of a (JL) FinFET at the scale of gate length 3 nm investigated on Silvaco TCAD EDA Tools. This (TF) FinFET is the truncation of the fin at it's lower end (near it's interface with substrate) to have good impact. Moreover, the material and width of substrate are decided such that there will be minimum leakage of drain current through it. The procurement of this work is reduction of SCEs marked as $S.S=66.5mV/dec$ and $\pmb{DIBL}=2.5\pmb{mV}/\pmb{V}$ at room temperature in case of TF-FinFET. The enhancement in device performance can be inspected by some more SCEs parameters, which actually vary when channel length get comparable to the depletion width of Source and drain junctions, such as drain current at OFF state (which found out to be decreased by 81.5 times in TF-FinFET at 300K), substrate current (which stood lowest at 500K and highest at 200K), switching ratio denoted by “ $\mathbf{I}_{\mathbf{ON}}/\mathbf{I}_{\mathbf{OFF}}$ ” (grown by 120 times in case of TF-FinFET at 200K) and the threshold voltage “ $\mathbf{v}_{\mathbf{th}}$ ” of the simulated devices (which was found to be 0.256 V for TF-FinFET and 0.148 V for conventional FinFET at 200K). These parameters are best observed between 200K to 300K.

PoisSolver: a Tool for Modelling Silicon Dangling Bond Clocking Networks

Abstract: Advancements in the fabrication of silicon dangling bonds (SiDBs) reveal a potential platform for clocked field coupled nanocomputing structures. This work introduces PoisSolver, a finite element simulator for investigating clocked SiDB systems in the SiQAD design tool. Three clocking schemes borrowed from prior work on quantum-dot cellular automata are examined as potential building blocks for a general clocking framework for SiDB circuits. These clocking schemes are implemented in SiQAD, and power estimates are performed with geometrically agnostic methods to characterise each clocking scheme. Clocking schemes using a 14 nm technology node are found to dissipate 10–100 µW cm-2at 1 GHz and 1-10W cm-2at 1 THz.

Intratumoral Gold Nanoparticle-Enhanced CT Imaging: An in Vivo Investigation of Biodistribution and Retention

Abstract: This study aims to evaluate the in vivo distribution of Gold Nanoparticles (GNPs) at different time points after intratumoral (IT) injection, exploiting their properties as contrast agents for Computed Tomography (CT). GNPs approximately 40 nm in diameter were synthesized with a surface plasmon peak at ~530 nm, capped with Bovine Serum Albumin (BSA) to improve colloidal stability, and characterized with standard methods. CT phantom imaging was performed to quantify X-ray attenuation as a function of GNP concentration and surface functionalization and to determine the appropriate particle dose for in vivo studies. Concentrated GNPs were intratumorally (IT) injected into Lewis Lung Carcinoma (LLC) solid tumors grown on the right flank of 6-week old female C57BL/6 mice. Ten days post-injection, follow up CT imaging was performed to assess the distribution and retention of the particles in the tumor. Using the CT attenuation quantification, images for each timepoint were segmented, and 3D volumes rendered, to conduct biodistribution analyses. The successful retention and permanence of the GNPs into the solid tumor after ten days suggests the significance of GNPs as a potential theranostic agent.

Mode Coupling and Rabi Splitting in Transdimensional Photonic Lattices

Abstract: We study the resonant response of a hybrid plasmonic-dielectric lattice and analyze mode coupling induced by the periodic arrangement. We design scattering elements out of multi-segment nanostructure allowing for subwavelength light confinement, and we study characteristic asymmetric spectral profile, show excitation of Fano resonances, and demonstrate peak (Rabi) splitting resulting from strong coupling of nanoantenna modes in the lattice.

TCAD Investigation of Gate - Lag Measurements on Conventional and π - Gate AlGaN/GaN HEMTs

Abstract: Dispersive effects that are evident in wide band gap semiconductors have undesirable fallouts with respect to the compressed drain current and output device power. In this paper, $\pi$ - Gate AlGaN/GaN HEMT architecture has been investigated and explored for minimizing the effect of gate - lag phenomenon so observed due to the surface states available on the AlGaN barrier layer. Comparisons demonstrate a reduction in drain current compression by 8% in case of π - Gate HEMT in comparison to the Conventional HEMT due to the donor like surface states at different ambient temperatures, thus indicating the suitability of the π - Gate HEMT architecture for high power and high frequency applications.

New Proficient Ferroelectric Nanosheet Line Tunneling FETs with Strained SiGe through Scaled n-epitaxial Layer

Abstract: We for the first time report ferroelectric based nanosheet line-tunneling field effect transistors (FeNLTFETs) by scaled n-epitaxial layer with Si 1-x Ge x as the source. The major engineering findings are shown by analyzing with physical governed factors to estimate the performance of FeNLTFETs. The line-tunneling mechanism with ferroelectric material (HZO) is properly tuned to improve the performance of ferroelectric line- TFETs. The suggested and simulated design is capable to deliver with the magnitude of Ion as 36.12 J.lA/J.lm, the impressive I Off of 94.31 aA/µm, and minimum and maximum subthreshold swings are of 3.75 mV/dec and 42.69 mV/dec, respectively. Notably, the estimated I on /I off is in the orders of 1011 on the scaled epitaxial ferroelectric nanosheet line-TFET (SEFeNLTFET) structure by using Sio.6Geo.4 as source.

Highly Efficient Nanostructured PtSe2 FET for Toxic Gas Detection

Abstract: Transition metal chalcogenides (TMDs) based FET sensors have gained tremendous attention due to their excellent electronic and physical properties. The detection of toxic gases such as NO 2 and NH3 are of paramount importance for human and environment. In this work, highly efficient nanostructured PtSe2 field-effect transistor (FET) is fabricated for toxic gas detection. The sensors exhibit very high response of 2220% and 675% at very low concentration of 10 ppm and 1 ppm, respectively, of NO 2 . The selectivity test was done in cross-environment of NH3. These results indicate the promising toxic gas detection by PtSe2 FET sensor.

Electrical transport in two-dimensional PdSe2 and Mos2 nanosheets

Abstract: We investigate the effect of pressure and gas species on the electrical transport in nanosheets of palladium diselenide (PdSe2) and molybdenum disulfide (MOS2), used as the channel of back-gate field-effect transistors. Air pressure can control the carrier polarity in PdSe2 devices and the dominant n-type conduction in a high vacuum can reversibly transform in p-type transport at atmospheric pressure. Structural defects facilitate gas adsorption, which widens the hysteresis of the transfer characteristics. For Mos2 the hysteresis has a monotonic dependence on gas adsorption energy. We investigate the effect of low-energy electron irradiation and find that few tens e−/nm2 fluence can significantly change the transistor characteristics. Finally, the field emission currents from both PdSe2 and Mos2 nanoflakes are measured. The first experimental observation of the gate modulation of the field emission current from a Mos2 monolayer is reported. Such a finding constitutes the proof-of-concept of a field-effect transistor based on field emission and paves the way for new applications of 2D materials in vacuum electronics.

Single Electron Control by a Uniform Magnetic Field in a Focusing Double-Well Potential Structure

Abstract: Double-well potential structures provide rich capabilities for single electron control via different physical characteristics of the potentials and the electron state. Here, we investigate the effect of a uniform magnetic field on the electron state interference pattern manifesting in a focusing double-well potential structure by conducting Wigner quantum transport experiments. We analyze the electron density and the negativity of the Wigner function and show how the magnetic field controls the electron state but also destroys the coherence of the evolution dynamics. Our work contributes to the fundamental understanding of magnetic field based single electron control mechanisms and sheds light on the critical decoherence processes.

Development and Characterization of a Piezoresistive Polyurethane/GNP Coating for Strain Sensing Applications

Abstract: In this work a simple cost-effective process is described to obtain a highly piezoresistive coating, consisting of sprayable water-based polyurethane (PU) paint filled with graphene nanoplatelets (GNPs). We investigated the morphology of the produced nanomaterials (i.e. cross-section and top surface) using a Field Emission Scanning Electron Microscope (FE-SEM). The rheological features of the polymeric blend loaded with 3.5 wt% of GNPs were analyzed at different concentrations of water (up to 20 wt%) in order to achieve a viscosity suitable for air-spraying. Moreover, the effect of humidity on the electrical resistance variation of the cured nanocomposite films was investigated and limited through the use of a covering agent. The stability of the PU/GNP based sensors protected with the covering agent was assessed repeating the same humidity test after four months. The sensor's piezoresistive response was obtained through three-point flexural tests and dc volt-amperometric measurements. The results of the electromechanical tests showed an increasing sensitivity of the sensor with the applied deformation and a maximum gauge factor of ~17 at 1% of strain, thus demonstrating the feasibility of the paint for strain sensing in structural health monitoring applications.

Printed Functionality for Point-of-Need Diagnostics in Resource-Limited Settings

Abstract: The work presented details micro and nano technologies for point-of-need health and environmental diagnostics in resource-limited settings, specifically in Southern Africa. The challenges faced in these settings have limited the effectiveness of point-of-need diagnostic solutions. By combining the growing fields of paper-based diagnostics and printed electronics, the extensive possibilities of functional printing can be utilized to develop novel, low-cost solutions for improving the quality of life of those who need it most. Examples of the research progress made in South Africa are presented, with a map for the way forward, encompassing the different technologies, skills and manufacturing processes required.

Employing Sorting Nets for Designing Reliable Computing Nets

Abstract: Recently, it was suggested that optimal sorting nets (which can trivially be mapped onto hardware) could be used to design highly reliable networks/systems. Sorting nets correspond to particular sorting algorithms, but it is their associated connectivity graph which seems to lead to highly reliable (minimal) two-terminal networks. Using the concept of associated connectivity graph we were able to link a reliability polynomial to any (optimal) sorting net. Here, we are going to thoroughly compare the two-terminal reliability polynomials associated to the connectivity graphs of very small optimal sorting nets, with the reliability polynomials of Moore-Shannon hammocks of similar size, as well as with size-equivalent compositions of series and parallel networks. These meticulous comparisons were done for getting a better understanding of the reliability of particular optimal sorting nets. The main conclusion is that small optimal sorting networks should be considered and might be useful for designing highly reliable computing systems.

Electric and Spectral Properties of Solid Water-Nanocellulose Systems in a Wide Range of Temperatures

Abstract: We report gravimetric, electric, and spectral properties of the solid-state water-nanocellulose systems with different water content. The systems with the nanocellulose content of 0.15, 0.3, 0.6, 96.6, and 97.3% undergo dielectric relaxation at temperatures between −100 and 0 °C, whose nature differs from that of the dielectric relaxation in pure water. The relaxation process in water-nanocellulose systems was found to be due to the dipole thermal polarization. This process is determined by the behavior of the surface layers of the nanocrystals, surrounded by the hydrated shell; its mechanism is due to the conformational motion of the methylol groups on the surface of the nanocellulose crystals.

Algal Extracellular Vesicles for Therapeutic Applications

Abstract: Extracellular vesicles (EV) are nano biomolecules released by the most type of the plant and animal cells, which have an important role in the cell to cell communications. EVs derived from these cells have tremendous therapeutic applications as these can efficiently deliver cargos to the target cells. In this study, the production and characterization of EVs from sustainable source of green algae is discussed. Their advantage of being cost-effective and production in higher quantity and relatively simple method of extraction could have potential applications as the drug delivery for several diseases such as cancer, neural disorders, inflammation, infectious, allergic diseases, etc. These extracellular vesicles perhaps could be loaded with a therapeutic agent and can be coated with drugs to target specific tissue, organ, or cell. Subsequently, pharmaceutical compositions can be coated to these extracellular vesicles, thereby; they can be used for monitoring, diagnosis and treating purposes.

Role of Interface Energetics and Off-diagonal Disorder in Bulk Heterojunction Organic Solar Cells

Abstract: Organic Solar Cells (OSCs) have been extensively studied regarding the impact of morphology and energetic disorder on power conversion efficiency (PCE). The impact of energetic disorder is well understood but the effect of disorder in molecular coupling (off-diagonal) and energetic disorder at the interface still needs investigation. We present a kinetic Monte Carlo (kMC) model to study the role of interface energetics and off-diagonal disorder on solar cell performance. We first analyze the impact of different energetic disorder at the acceptor(A)-donor(D) interface on the device performance. Our results reveal that the interface properties control the Voc and efficiency. For higher interface disorder, recombination increases and the Voc is reduced. We further demonstrate the impact of variable off-diagonal disorder at fixed interface disorder on the device. The results show that at higher off-diagonal disorder, recombination, as well as Voc, is reduced. The presented results allow a better understanding of the importance of the structural order at the interface for OSCs.

Electric Field Induced Liquified Mass Transport Phenomenon in Chromium Thin Films on Application of an Alternating Potential

Abstract: Electromigration phenomenon might be employed in creation of patterns on metallic thin films in the micro range or even in the nano range dimensions [1], [2]. This paper puts forward a non- conventional form of mass transfer that has been observed in Chromium thin films under the effect of high current densities when an alternating field is applied. As it has been observed, the high density current, along with the accompanying heat generation, fuels a reaction in which the metal reacts with the ambient air and produces a fluidic compound in a ring-like manner from the electrode. Within the domain of this paper, ramp wave alternating electric field is used with the frequency ranging from 350 Hz to 700 Hz with a stepping of 50 Hz. The velocity of flow, as well as the electrical current are measured with respect to time throughout the duration of the experiment. Added to that several interesting observations were also made. The work reported in this paper will aid in apprehending the flow behavior, helping to get a better grip over the electromigration assisted nanolithography process.

Role of Ion-Assisted Recombination and Grain Boundaries in Perovskite Solar Cell Hysteresis and Efficiency

Abstract: Organic-inorganic hybrid perovskite (OIHP) solar cells are one of the fastest-growing solar cell technologies ever. OIHPs offer a wide range of bandgaps, wide optical absorption and low-cost deposition, making them an ideal candidate for solar cells. Despite the amazing properties of these materials, the perovskite solar cell performance is hampered by grain boundaries, traps, and hysteresis behavior of current-voltage (JV). Though the exact mechanism behind the hysteresis is still unknown, ionic movements in the perovskite film are considered to be the primary reason behind it. We present a drift-diffusion (DD) model to study the role of cation-mediated non-radiative recombination in the JV hysteresis in CH3NH3PbI3 cells. We study how the mobile cations can trap electrons leading to the JV hysteresis and poor performance of the cell. Impact of cation-electron trapping constant and the JV scan rate is investigated. We also simulate how the accumulation of mobile ions at the grain boundaries and interfaces limits the solar cell output current. When the ions are distributed in the bulk grains, they hardly affect the cell performance. When they start accumulating at the grain boundaries, the Jsc drops rapidly. The presented results give an insight into the effect of grain boundaries, and cation-mediated recombination as a possible reason for the JV hysteresis in perovskite solar cells.

Combined effect of proteins and AgNPs on the adhesion of yeast Candida albicans on solid silica surfaces

Abstract: Research and development of new biomaterials has considerably increased in the last ten years. Description of their properties involves among others their interaction with proteins. Due to the exposure of proteins to non-biological solid surfaces the relationship between protein structure and function might be modified. The conformation and arrangement of the adsorbed proteins on the surface further control the subsequent biological processes and thus determine the biological response to the material. In this work we present the impact of silver nanoparticles (AgNPs) embedded in the near-surface of thin silica layers on the adhesion forces of Candida albicans IP48.72 in conditioned by different proteins environment. Depending on the nature of proteins the effect can be opposite: The Bovin Serum Albumine (BSA) decreases the yeast adhesion on solid silica surfaces while the Fibronectin (Fn) favors it. It is also found that the AgNPs, when embedded in the near-surface of thin silica layers, impair the adhesion forces of C. albicans through the release of silver ions and lead the cell dead.

Nanodroplet-Mediated Intravascular Sonothrombolysis: Cavitation Study

Abstract: Nanodroplets mediated sonothrombolysis has the potential to improve thrombolytic outcomes and minimize the need for thrombolytic drugs. Our group has developed a forward-viewing intravascular transducer which can perform contrast agent mediated sonothrombolysis. Most applications of nanodroplets mediated sonothrombolysis are applied by an external transducer, which cannot access locations blocked by bones or gassy organs, thus greatly limiting its usage. The purpose of our study was to demonstrate the feasibility of using nanodroplets with our small aperture intravascular transducers, which would allow access to a wide range of locations. Passive cavitation detection was performed to determine the minimum peak negative pressure output necessary for nanodroplet mediated sonothrombolysis and initial clot lysis tests were performed. The stable cavitation dose increased with increasing peak negative pressure output, with there being a higher stable cavitation dose at 0.9 MPa and 1.2 MPa compared to controls. The inertial cavitation dose was higher at 0.6 and 0.9 MPa compared to the control group. In our proof-of-concept demonstration, nanodroplets mediated sonothrombolysis presented a mass decrease of 55 ± 1% compared to 29 ± 6% for the control group (p=0.02). We demonstrated that it was feasible to deliver nanodroplet mediated sonothrombolysis using the small aperture intravascular transducers.

Stripping Voltammetry of Nanoscale Films of Cu–Zn, Cu–Sn, Zn–Ni Alloys

Abstract: The chemical and phase composition of the thin films of Cu–Zn, Cu-Sn, and Zn-Ni alloys obtained from pyrophosphate-citrate, pyrophosphate-trilonate, and ammonia-glycinate electrolytes, respectively, was determined by the method of stripping voltammetry. It is shown that increase in current density of Cu–Zn alloy films deposition leads to the α-phase content decrease, the β-phase content stabilization, the e-phase content increase, and appearance of an extremum in γ-phase content, while content of γ1-phase of Zn-Ni alloy decreases, γ2-phase content increases, and total nickel increases due to an increase in the content of β-phase in the films. Increase in Cu-Sn alloy films deposition time leads to increase in α-phase content, decrease in e-phase content; dependences of η-phase content and total tin have a maximum at films thickness of 350 nm.

Increased Dielectric Strength of Polyimide/Silicon Dioxide Nanocomposites at Cryogenic Temperatures

Abstract: Polyimide/silicon dioxide nanocomposites were synthesized and tested dielectrically at both room and cryogenic temperatures. The dielectric strength of the nanocomposites showed significant increase from about 150 kV/mm at room temperature to roughly 300 kV/mm at the cryogenic temperature. This increase in dielectric strength is a result of the contraction of the host polymer around the embedded nanoparticles, which shortens the mean free path of electrons as well as the distance needed for electrons to accelerate to induce avalanche breakdown. The contraction of the host polymer also reduces the overlapping of the transition region, the outermost layer of the multi-core model, between individual nanoparticles. The findings from our experimental results and multi-core model can potentially advance the field of cryogenic dielectrics.

Flexible Graphene Based Polymeric Electrodes for Low Energy Applications

Abstract: In this work, novel flexible metal-free polymeric cathode electrodes are developed through a cost-effective procedure for low energy generation applications. For this purpose, a nanocomposite film made of poly vinylidene fluoride (PVDF) filled with graphene nanoplatelets (GNPs) is produced through an easy process, without the use of any chemical or physical doping agent. The fabricated PVDF/GNP nanocomposite films are morphologically and chemically characterized and their applicability as polymeric electrodes is investigated through electrochemical tests.

Impedimetric Detection of Bacteria Using Hierarchical 3D Nanostructured Gold

Abstract: Impedimetric electrochemical sensing offers direct, label-free, cost-effective, accurate, and rapid detection of biological analytes. Among different types of nanostructured platforms, hierarchical structures of gold have proven to be beneficial for impedimetric and direct diagnosis of bacteria. In this research, a two-step electrodeposition method was used to achieve hierarchical nanostructures of gold for impedimetric distinction of E. coli-k12. The current observations demonstrate that the two-step electrodeposition method can convert sharp and needle-shaped structures of gold into curved and smooth structures that are able to detect bacteria, with enhanced sensitivity. The results of Electrochemical impedance spectroscopy (EIS) showed a limit of detection of approximately 90 CFU in 30 µl of solution and a linear range of detection between 3×103and 3×107CFU mL-1 for the final sensor. In addition, this structure can detect bacteria in less than 10 minutes. Ultimately, this ultrasensitive label-free bacteria sensor, based on a novel engineered hybrid method, opens interesting avenues in bacteria sensing with exciting detection abilities. Keywords: E. coli bacteria, electrodeposition, hierarchical nanostructures of gold, electrochemical impedance spectroscopy (EIS).

Characterization and Analysis of Two-dimensional Hydrogenated Nanocrystalline-diamond Metal Oxide Semiconductor Field Effect Transistor (MOSFET) using Different Surface Charge Models with Device Simulation

Abstract: Thanks to the unique properties, nanocrystalline-diamond is a valuable material that is widely used in nano-electronic device fabrication to enable the new promising power device applications in the near future. In general, the hydrogenated-(C-H) nano-diamond metal oxide semiconductor (MOSFET) depicts the normally- on status (depletion mode). In this paper, to confirm normally-on operation and show the characterization of normally-off operations with a controlled gate of the power device and study the corresponding impact, we simulate the two-dimensional (2D) C-H nano-diamond MOSFET under several surface charge models' impact. The enhancement mode, called normally-off, is attained to realize a safety point of the power device. The results also show the shifting tendency of the threshold voltage to a negative value with a positive charge model, given that, in principle, this state is impractical without a donor doping or oxidation layer.

Heavy Metals Removal Using Nanostructured Carbon-Based Composites in the Presence of Various Organic Compounds

Abstract: Due to intense development of civilization and human activity, there is a continuous increase of the heavy metals concentration in the environment. This phenomenon is particularly visible in inland surface waters, marine coastal waters, soil waters as well as shallow groundwater. Heavy metals are impurities that pose a particular threat to organisms. In plants, they may reduce nutrient uptake, which contributes to growth inhibition, chlorosis, and necrosis. In animals, heavy metals may damage kidneys and liver, disrupt nervous and cardiovascular systems, and lead to infertility and tumor growth. Taking these facts into account, it can be stated that effective removal of heavy metal ions from aqueous solutions is highly important. Innovative composites based on carbon can be the solution to the above problem. Due to their unique properties—large specific surface area, appropriate porosity, and high concentration of surface active centers—they assure excellent adsorption properties in relation to low- and high-molecular weight adsorbates such as metal ions, dyes, drugs, pesticides, and polymers. Sorbents composed of the core made of one or two heavy metals, and the shell consisting of carbon and silica is the special group of these materials. Some of them have magnetic properties, thanks to which the used solid covered with adsorbed impurities can be easily separated from the solution. Few studies on composite sorption capacity for heavy metal ions in the presence of other environmental pollutants (e.g., synthetic polymers, surfactants) were currently conducted. Nevertheless, this issue has not been sufficiently explored so far and requires further research.

Influence of elongation and washing on double-layer R2R-printed flexible electrodes for smart clothing applications

Abstract: Flexible electrodes are crucial for the growth of modern flexible electronics or smart clothing. Their ability to serve as sensing elements, deliver energy or transmit electrical signals in different conditions is essential for the evolution of wearables that will enrich our everyday life. In this study, we focus our efforts on understanding the impact of an additional protective layer on elongated and washed roll-to-roll printed (R2R) conductive flexible electrodes of various shapes. The electrical and morphological examinations provide information on the performance of the electrodes and materials during washing and elongation cycles. The acquired results indicate propitious electrode shapes as well as data concerning micro-scale cracking mechanisms, which are responsible for electrode performance degradation. The application of commercially available pastes and R2R printing methods allow the flawless utilization of the results and the fabrication of flexible and more reliable electronic components.

Field emission properties of molecular beam epitaxy grown AlGaN nanowires

Abstract: We investigate the field emission properties of AlGaN nanowires, grown on GaN nanowire templates on Si(111) substrate by means of radio-frequency plasma-assisted molecular beam epitaxy technique. The field emission measurement setup was realized inside the vacuum chamber of a scanning electron microscope equipped with piezo-driven metallic probe tips working as electrodes. Current-voltage characteristics were measured by precisely positioning a tip anode above the emitting AlGaN surface, with cathode-anode separation distance varied in the range 200–1500 nm. Experimental data are discussed according to the Fowler-Nordheim theory to confirm the field emission nature of the measured current and to estimate key figures of merit, such as field enhancement factor and turn-on field. We show that field emission curves become stable after electrical conditioning, that is after the burnout of individual protruding emitters. We demonstrate field enhancement factor as high as 250 for cathode-anode separation distance of 200 nm, and that it decreases for increasing distances. Similarly, minimum turn-on field of 19 V/µm is reported for a separation distance of 800 nm. Finally, we discuss the effect of a Schottky diode in a back-to-back configuration with the field emission device, that limits the exponential growth field emitted current.

Spectrum of Localized Quasi-Particle Interacting with Three-Mode Phonons

Abstract: Within the unitary transformed Hamiltonian of Frohlich type, using the retarded Green’s function method, the exact renormalized energy spectrum of a quasi-particle strongly interacting with three-mode polarization phonons is obtained at T = 0 K in the model of a system with a limited number of its initial states. The exact analytical expressions for the average number of phonons in the main and all satellite states of the system are obtained. Their dependences on the magnitude of the interaction between quasi-particle and both phonon modes are analyzed.

Optoelectronic Thinning of Transition Metal Dichalcogenides for Device Fabrication

Abstract: Atomically thin transition metal dichalcogenides (TMDCs) are promising materials for nanodevices due to their extraordinary electronic, optoelectronic, and mechanical properties. However, massive production of high-quality atomic monolayers of TMDCs remains challenging. Herein, we report a self-limiting optoelectronic thinning method for fabrication of monolayers of TMDCs and their micro/nanopatterns at the large scale and in a versatile manner. By properly choosing the wavelength of our working laser beams, we selectively excited electrons between indirect band gap of bulk or few-layer Mos2,which promoted the thinning of the TMDCs via electrochemical degradation. Once the Mos2reached atomic monolayers, our laser beam could not excite the electrons over the wider direct band gap. Therefore, the electrochemical reaction stopped and the Mos2remained as atomic monolayers.