Low Onset Voltage Research Articles

Donor-Acceptor Copolymers with 9-(2-Ethylhexyl)carbazole or Dibenzothiophene-5,5-dioxide Donor Units and 5,6-Difluorobenzo[c][1,2,5]thiadiazole Acceptor Units for Photonics.

Semiconducting polymers, particularly of the third generation, including donor-acceptor (D-A) copolymers, are extensively studied due to their huge potential for photonic and electronic applications. Here, we report on two new D-A copolymers, CP1 and CP2, composed of different electron-donor (D) units: 9-(2-ethylhexyl)carbazole or dibenzothiophene-5,5-dioxide, respectively, and of 4,7-bis(4'-(2-octyldodecyl)thiophen-2'-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole building block with central 5,6-difluorobenzo[c][1,2,5]thiadiazole electron-acceptor (A) units, which were synthesized by Suzuki coupling in the high-boiling solvent xylene and characterized. The copolymers exhibited very good thermal and oxidation stability. A copolymer CP1 with different molecular weights was prepared in order to facilitate a comparison of CP1 with CP2 of comparable molecular weight and to reveal the relationship between molecular weight and properties. The photophysical, electrochemical, and electroluminescence properties were examined. Intense red photoluminescence (PL) with higher PL efficiencies for CP1 than for CP2 was observed in both solutions and films. Red shifts in the PL thin film spectra compared with the PL solution spectra indicated aggregate formation in the solid state. X-ray diffraction measurements revealed differences in the arrangement of molecules in thin films depending on the molecular weight of the copolymers. Light-emitting devices with efficient red emission and low onset voltages were prepared and characterized.

Numerical investigations to determine onset voltages in monolithic electrospray thruster chips with electrospray cavities

We present electrostatic simulations determining onset voltages of a new electrospray thruster that expands on previous work [Jones et al., J. Electrostat. 108, 103487]. The design integrates extraction grid and emitter chip in one monolithic device, with cylindrical “electrospray cavities” excavated around emitters. The cavities electrically isolate emitter and grid (which is immovable/inflexible), and intercept stray propellant to prevent overspray and shorting. Simulations yield onset voltages of less than 250 V, significantly lower than recently reported values. The concept demonstrates improved robustness, increased resilience to failure, remarkably low onset voltages, and can be readily fabricated with established laser micromachining techniques.

Atomic layer deposition of Er-doped yttrium aluminum gallium garnet nanofilms with tunable crystallization and electroluminescence properties.

Polycrystalline erbium-doped Y3(AlxGa1-x)5O12 (Er-YAGG) nanofilms with various Al/Ga compositions are deposited on silicon using atomic layer deposition followed by annealing at different temperatures. The Al/Ga ratios and the corresponding annealing temperatures required for crystallization are confirmed by investigating the diffraction patterns and micro-morphologies. The co-alloying of Al and Ga compositions controllably changes the lattice constant and impacts the grain growth. The crystal-field splitting of doped Er3+ ions is also modified, manifesting different electroluminescence (EL) spectra that also indicate the crystallization of garnet matrices. The EL performance of a device based on the Y3Al2Ga3O12 nanofilm (1.39 at% Er dopant) annealed at 900 °C is improved due to the adjustment of morphology and microstructural perturbations that are beneficial for radiative transition. The optimal EL device exhibits a low onset voltage of ∼25 V and a maximum external quantum efficiency of 3.29%. The excitation cross-section under electrical pumping is estimated to be 1.18 × 10-15 cm2. The carrier transport of these co-alloyed Er-YAGG devices conforms to the Poole-Frenkel mechanism. Both the EL decay lifetime and the device operation time increase with the incorporation of Ga within the Er-YAGG nanofilms. These Er-YAGG devices with tunable optoelectronic properties manifest promising potential for the engineering of light sources compatible with CMOS technology.

Rare earth Nd-doping lead-free double perovskite Cs2AgBiBr6 films with improved resistive memory performance

Lead-free double perovskites have been an excellent candidate for resistive memories due to their mixed electronic-ionic properties, remarkable ambient stability and nontoxicity. However, the studies on resistive memories of rare-earth ion doping lead-free double perovskite are scarce to date. Here, we report the lead-free double perovskite Cs 2 AgBiBr 6 films with tuning rare earth Nd 3+ content by the vacuum sublimation and solution processing. The X-ray diffraction (XRD) pattern and scanning electron microscopy (SEM) confirm that Nd-doped Cs 2 AgBiBr 6 films show high crystallinity and phase purity. We also systematically investigate the resistive memory properties of the resulted Cs 2 AgBiBr 6 films doped by different content Nd 3+ . The resistive memory devices demonstrate a typical write-once-read-many-times (WORM) behavior with low on-set voltage and long retention time. Particularly, the ON/OFF ratio of Nd-doped Cs 2 AgBiBr 6 film is 1000 times higher than that of the undoped Cs 2 AgBiBr 6 film. This study exhibits that Nd-doped Cs 2 AgBiBr 6 film provide a new material platform for lead-free perovskite-based application in future electronics and optoelectronics. • The Cs 2 AgBiBr 6 film doped by different content rare earth Nd 3+ is reported. • The simplest sandwich-like structure device based on doping Cs 2 AgBiBr 6 is designed. • The resistive memory device demonstrates a typical WORM behavior. • The ON/OFF ratio of Nd-doped film is 1000 times higher as compared to undoped film.

Understanding the Degradation Mechanisms of Lithium Ion Batteries Using in-Situ Multi-Scale Diffraction Techniques

Advanced Li-ion batteries adopting new cathode chemistries are required for the successful widespread transition to electric vehicles (EVs) and renewable energy sources, aiming for high energy density, long cycle life, and good rate capability. Commercial candidates for EV batteries include Ni-rich Li(NixMnyCo1−x-y)O2 (NMC) cathodes, with Ni:Mn:Co ratios of 8:1:1 (NMC811) and higher. These are favored because of their high specific capacity (~ 200 mAh g-1)and reduced cobalt content. Despite all of the advantages, these materials suffer from a range of degradation modes, many of which are associated with the redox and crystallographic behavior at high states of charge. In particular, Ni-rich cathodes suffer from several limitations, such as rapid capacity fade in comparison to NMC stoichiometries with lower Ni content. In addition, they also have a lower onset voltage for oxygen release and subsequent surface reconstruction leading to the formation of spinel and rock salt phases which impede (de)lithiation and therefore the achievable capacity of the cell.1 Crystallographic properties of electrode materials are intrinsically linked to the electrochemical performance of the cell. NMC materials suffer from anisotropic changes in the crystal structure during cycling which induces strain and leads to issues such as crack formation, expediting degradation. One method to tackle capacity fade is to switch to single-crystal morphologies (particle size 1-3 μm) which have better mechanical stability than conventional polycrystalline morphologies (secondary agglomerate particles ~ 10 μm made up of primary particles which are 100 nm – 1 μm in size) and have less propensity to form extensive rock-salt layers. It is thought that the single-crystal morphology helps to reduce stress in the material as the anisotropic stress in polycrystalline cathodes is concentrated at grain boundaries. However, there is still a limited understanding of the subtle mechanistic differences between the two materials during cycling.2 A multi-scale approach is required to gain a more comprehensive understanding of the degradation mechanisms at play and how they initiate and propagate. In this work, synchrotron diffraction methods were employed at the crystal, particle and cell scale using a variety of techniques including in-situ Bragg Coherent Diffraction Imaging (BCDI), 3D-XRD and operando high-resolution XRD. Intra-particle, inter-particle and electrode level heterogeneities were observed during cycling, both in pristine and aged samples. It is believed that these heterogeneities accelerate the loss of performance at the cell level by inducing crack formation which can then be observed in X-ray computed tomography data acquired in simultaneous lab studies. The overarching goal of these investigations is to add to the understanding of complex degradation mechanisms for Ni-rich layered transition metal oxide cathodes, ultimately aiding in the informed development of future battery electrode materials.

Tunable lanthanum doping in double perovskite films for read-only memory

Rare earth ions have been widely investigated as active dopants in various materials because of their distinct optical, electronic and magnetic properties. Halide perovskite resistive memories have attracted increasingly recent interest for tremendous potential applications in computation and data storage techniques. However, it remains unexplored to implement rare earth doping strategy for tuning perovskite resistive memories. Here, we report read-only memories based on environment-friendly and air-stable lead-free double perovskite Cs2AgBiBr6 films, which is particularly tuned by rare earth La3+ doping. We use the vacuum sublimation and solution processing method to obtain Cs2AgBiBr6 crystals doped by different content La3+, and fabricate resistive memory devices based on doped Cs2AgBiBr6 films. The simplest sandwich-like structure composed of ITO/La-doped-Cs2AgBiBr6/Ag only is designed in cross-bar array architecture with high-integration and simple operation. The resistive memory device of La-doped Cs2AgBiBr6 films demonstrate a typical write-once-read-many-times (WORM) behavior with low onset voltage of 1 V and long retention time of 12000 s. In particular, the ON/OFF ratio of the La-doped Cs2AgBiBr6 film is 100 times higher than that of the undoped Cs2AgBiBr6 film. This study provides a new insight to design and manipulate memory devices based on lead-free halide perovskite materials through doping effect of rare earth ions.

Current transport mechanism of AlGaN-channel Schottky barrier diode with extremely low leakage current and high blocking voltage of 2.55 kV

This Letter presents work on lateral AlGaN-channel Schottky barrier diodes (SBDs) with impressive reverse blocking characteristics and low onset voltage (VON). A low reverse current (IR) of 28 nA/mm and low VON of 0.60 V are obtained by utilizing an AlGaN back barrier layer with high Al composition and low work function metal as the anode. The fabricated AlGaN-channel SBD with an anode–cathode distance (LAC) of 30 μm achieves a high blocking voltage of 2.55 kV and a power figure-of-merit of 363 MW/cm2. Meanwhile, the current transport mechanism of AlGaN-channel SBDs goes through thermionic emission, thermionic field emission, and trap-assisted tunneling as the reverse bias is gradually increased. The thermal activation energy (EA) is calculated to be 141.3 meV at high reverse bias. IR at 475 K is only 3 μA/mm, which shows an adequate barrier height for rectifying at high temperature even with low VON. The AlGaN-channel SBDs show great promise for next-generation power electronics with balanced forward and reverse characteristics.

Fundamental investigation of unipolar and RF corona in atmospheric air

Unipolar (DC) and radio frequency (RF) corona at 3.3 MHz is studied at centimeter-sized gaps in a needle-plane geometry in atmospheric air at room temperature. Positive and negative corona using pure tungsten electrodes with varying tip angles revealed a lower onset voltage for the needle with the smaller included angle. The RF corona onset voltage and corresponding time delay were measured for a series of needles composed of pure tungsten or 2% lanthanated tungsten. The corona onset, established when the first instance of UV photon emission is detected via photomultiplier tube, occurred primarily during the negative half cycle of the applied RF voltage for pure tungsten needles. In contrast, with lanthanated tungsten needles, such preference was not observed. No distinguishable difference in onset voltage between pure tungsten and lanthanated tungsten was found, indicating that adding a small amount of lanthanum to tungsten has a negligible impact on the onset voltage at 3.3 MHz frequencies for electrodes at room temperature.

The Influence of Recessed Floating Metal Rings Structure on Electrical Properties of AlGaN/GaN Schottky Barrier Diodes

AlGaN/GaN lateral Schottky barrier diodes (SBDs) with the nonrecessed and recessed floating metal rings (FMR) structure are fabricated and electrically characterized to study the influence of recessed FMR structure. The recessed FMR SBDs (RFMR‐SBDs) exhibit the lower onset voltage (V ON) and higher forward current (I F) at the anode of 3 V than the nonrecessed FMR SBDs (FMR‐SBDs). More importantly, the breakdown voltage (V BR) of the RFMR‐SBDs is 1980 V, which has a significant improvement compared with the FMR‐SBDs of 1540 V. However, the specific on‐resistance of the RFMR‐SBDs is higher than FMR‐SBDs. Furthermore, the electric field distributions of different structures are simulated by Silvaco software to analyze the mechanism of improving breakdown voltage. The results show that the breakdown voltage improvement is due to the broader depletion region in the RFMR‐SBDs at the breakdown voltage. Moreover, the electric field distributions of the RFMR‐SBDs and FMR‐SBDs with three FMRs are discussed further.

Graphene quantum dots as shallow traps in a high-k polymer matrix for bipolar resistive switching

Graphene quantum dots (GQDs) have broad applications in electronic and photonic devices. As a typical zero-dimensional material, a GQD has a stronger quantum confinement effect than do two-dimensional graphene or one-dimensional graphene nanoribbons, and provide efficient charge trapping sites, which are useful in nonvolatile memory devices. Here, we report the fabrication of 30-nm-thick GQD-blended high-k polymer cyanoethylated pullulan (CEP) thin films sandwiched between an Al top electrode and an indium tin oxide (ITO) bottom electrode. Bipolar resistive switching behavior was observed with a low onset (−1.7 V) and offset (1.3 V) voltages. The resistive switching behavior originates from shallow traps that induce space-charge-limited current conduction. The morphology, crystallinity and photoluminescence of the GQDs were also studied by atomic force microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The CEP/GQD blended films may have applications in nonvolatile resistive memory devices.

Multifunctional donor–acceptor conjugated polymers containing isoindigo and benzothiadiazole moieties for electrochromic, photoelectric sensor, 2,4,6-trinitrophenol detection and resistance memory device

Six novel donor–acceptor conjugated polymers were designed and synthesized by the Stille coupling reaction of triarylamine derivatives as donor units with isoindigo derivative or benzothiadiazole as acceptor units. These polymers have good solubility and film-forming properties in common organic solvents. The char yields of polymers in nitrogen atmosphere at 800 °C range from 34 to 60%. In particular, these conjugated polymers exhibit high photoluminescence (PL) quantum efficiency (up to 42.9%). These polymers demonstrate two pairs of redox peaks with low onset voltages (0.51 V vs. Ag/AgCl for P5) and narrow band gaps (Eg = 2.52 ~ 2.95 eV). The colors of all polymer films change significantly with the applied voltage increasing. Moreover, the polymers show high coloring efficiency (up to 163%) and maintain good electrochromic (EC) cycle stability over 500 s. In addition, excellent results in terms of memory storage (ON/OFF = 1.2 × 104), 2,4,6-Trinitrophenol (TNP) detection (Ksv = 45,790 M-1) can meet the requirements of multifunctional materials.

One-dimensional CO9S8-V3S4 heterojunctions as bifunctional electrocatalysts for highly efficient overall water splitting

Development of cost-effective, active and durable electrocatalysts for overall water splitting is still a huge challenge. Herein, we have constructed one-dimensional (1D) cobalt sulfide and vanadium sulfide heterojunction nanowires arranged on carbon cloth (Co9S8-V3S4/CC) as bifunctional electrocatalysts for the efficient overall water splitting. The 1D wire-structured Co9S8-V3S4 heterojunctions possess large surface area, plentiful active sites and rapid transport of electrons/reactants and the release of gas. Importantly, the electron transfer from Co9S8 to V3S4 occurs at the interface due to the strong electronic coupling effect in Co9S8-V3S4 heterojunction, in which the electron-attracting V3S4 (V2+) optimizes the adsorption of H* active species for hydrogen evolution reaction (HER), while the electron-losing Co9S8 (Co3+) responds to the enhancement of oxygen evolution reaction (OER) activity. Co9S8-V3S4/CC exhibits low overpotentials of 85 and 232 mV at 10 mA cm−2 and small Tafel slopes of 51 and 59 mV dec−1 for HER and OER, respectively. Especially, the electrolyzer with Co9S8 V3S4/CC as both the anode and cathode requires low onset voltage of 1.35 V and cell voltage of 1.53 V at 10 mA cm−2 and exhibits high Faradaic efficiencies and robust stability. It can be driven by a solar cell (1.53 V) for continuous production of hydrogen and oxygen. This study highlights the design of 1D sulfide heterojunction in pursuit of highly efficient electrocatalysts for overall water splitting.

Tuning Optical Properties by Controlled Aggregation: Electroluminescence Assisted by Thermally-Activated Delayed Fluorescence from Thin Films of Crystalline Chromophores.

Several photophysical properties of chromophores depend crucially on intermolecular interactions. Thermally‐activated delayed fluorescence (TADF) is often influenced by close packing of the chromophore assembly. In this context, the metal‐organic framework (MOF) approach has several advantages: it can be used to steer aggregation such that the orientation within aggregated structures can be predicted using rational approaches. We demonstrate this design concept for a DPA‐TPE (diphenylamine‐tetraphenylethylene) chromophore, which is non‐emissive in its solvated state due to vibrational quenching. Turning this DPA‐TPE into a ditopic linker makes it possible to grow oriented MOF thin films exhibiting pronounced green electroluminescence with low onset voltages. Measurements at different temperatures clearly demonstrate the presence of TADF. Finally, this work reports that the layer‐by‐layer process used for MOF thin film deposition allows the integration of the TADF‐DPA‐TPE in a functioning LED device.

Preparation and improved photoelectrochemical properties of InGaN/GaN photoanode with mesoporous GaN Distributed Bragg reflectors

We fabricate the large-area and highly reflective mesoporous GaN (MP-GaN) Distributed Bragg reflectors (DBRs) via an electrochemical etching technology in HNO3 solution for the first time and then use the DBRs as the template in growth of InGaN/GaN structure by the metal organic chemical vapor deposition (MOCVD) technology. The InGaN/GaN structure with MP-GaN DBRs acts as the photoanode during photoelectrochemical (PEC) water splitting experiments in 1 M HBr solution for the first time. Compared to the sample without MP-GaN DBRs, the InGaN/GaN structure with the MP-GaN DBRs presents significantly increased photoluminescence (PL) intensity, which is attributed to light reflection effect of the bottom MP-GaN DBRs and improved internal quantum efficiency (IQE) of the multiple quantum wells (MQWs) layer. More interestingly, the InGaN/GaN structure with the MP-GaN DBRs presents markedly improved PEC properties such as a low onset voltage (−0.61 V vs. RHE), a 4.5-fold enhancement in photoconversion efficiency and good stability.

π-Conjugated twin molecules based on 9,9-diethyl-1-phenyl-1,9-dihydrofluoreno[2,3-d]imidazole module: synthesis, characterization, and electroluminescence properties

A series of well-defined, π-conjugated twin molecules by connecting two 9,9-diethyl-1-phenyl-1,9-dihydrofluoreno[2,3-d]imidazole units via an ortho-, meta-, or para-benzene with high quantum efficiency of fluorescence is synthesized and fully characterized. The detailed thermal, electrochemical, photophysical, and electro-luminescence properties have been investigated. The electro-luminescence properties of the obtained materials are studied by fabricated the device using the configuration ITO/HATCN (5 nm)/NPB (20 nm)/TCTA (10 nm)/CBP: 5% doping (20 nm)/TMPYPB (40 nm)/LiQ (1 nm)/Al (80 nm). The doped OLED based on the compound with para-benzene as the emitting layer shows the best performance with the maximum current efficiency of 2.30 cd/A, maximum power efficiency of 1.52 lm/W, located in the deep-blue region with CIE (x, y) value of (0.1572, 0.0587) with relatively lower onset voltage of 4.25 V.

Space charge limited conduction mechanism in GaAsSb nanowires and the effect of in situ annealing in ultra-high vacuum

In this work, the first observation of the space charge limited conduction mechanism (SCLC) in GaAsSb nanowires (NWs) grown by Ga-assisted molecular beam epitaxial technique, and the effect of ultra-high vacuum in situ annealing have been investigated. The low onset voltage of the SCLC in the NW configuration has been advantageously exploited to extract trap density and trap distribution in the bandgap of this material system, using simple temperature dependent current–voltage measurements in both the ensemble and single nanowires. In situ annealing in ultra-high vacuum revealed significant reduction in the trap density from 1016 cm−3 in as-grown NWs to a low level of 7 × 1014 cm−3 and confining wider trap distribution to a single trap depth at 0.12 eV. A comparison of current conduction mechanism in the respective single nanowires using conductive atomic force microscopy (C-AFM) further confirms the SCLC mechanism identified in GaAsSb ensemble device to be intrinsic. Higher current observed in current mapping by C-AFM, increased 4 K photoluminescence (PL) intensity along with reduced full-width half maxima and more symmetric PL spectra, and reduced asymmetrical broadening with increased TO/LO mode in room temperature Raman spectra for in situ annealed NWs again attest to effective annihilation of traps leading to the improved optical quality of NWs compared to as-grown NWs. Hence, the I–V–T analysis of the SCLC mechanism has been demonstrated as a simple approach to obtain information on growth induced traps in the NWs.

Highly emissive fluorene and thiophene based π-conjugated A-alt-B copolymers: Synthesis, characterization and electroluminescence properties

Highly soluble and emissive fluorene and thiophene based A-alt-B type π-conjugated polymers, P1 and P2 have been successfully synthesized through Pd(0)-catalyzed Suzuki coupling polymerization by varying alkyl substitution at 3-position of thiophene. The synthesized cyan-emissive fluorene based π-conjugated polymers have been unambiguously characterized by various spectroscopic tools such as FTIR, multinuclear NMR as well as tetradetector GPC having molecular weight (Mn) 18.2 and 20.8 kDa with the polydispersity indices of 1.32 and 1.35 respectively. The detailed thermal, electrochemical, photophysical and electroluminescence properties of the polymers have been investigated. The highly emissive nature of the synthesized polymers even in solid state prompted us to explore its application as active materials in organic light emitting diodes (OLEDs). The electroluminescence properties of the obtained materials are studied by fabricated the device using the configuration ITO/PEDOT:PSS (50 nm)/P1-P2 (80 nm)/BCP (40 nm)/Al (100 nm). P1 and P2 exhibit bright cyan electroluminescence with CIE of (0.19, 0.29) and (0.21, 0.31) respectively with relatively lower onset voltage of 4 V.

Experimental study on electrostatic removal of high-carbon particle in high temperature coal pyrolysis gas

A high-temperature electrostatic precipitator (ESP) presents a good solution for hot gas cleaning, which can remove fly ash from pyrolysis gas at temperatures higher than the tar dew point. In this paper, the characteristics of negative DC corona discharge in air and simulated coal pyrolysis gas were studied. The removal of coal pyrolysis furnace fly ash (ash A) was investigated and compared with that of coal-fired power plant fly ash (ash B) in ESP with a temperature ranging from 300 K to 900 K. The current density of simulated gas was higher than that of air under the same discharge voltage and at different temperatures. The simulated gas also had a higher spark voltage and a lower onset voltage compared with air. The fractional collection efficiency of ash A was lower for particles with diameters of larger than 0.1 µm at high temperature, compared with ash B. A lower collection efficiency in simulated gas was obtained for particles with diameters of less than 0.1 µm compared with air. The collection efficiency of submicron particles in simulated gas was usually higher than it in air, especially for particles with diameters of less than 0.04 µm. In simulated gas, the overall collection efficiency of ash A was obviously lower than that of ash B, especially at high temperature. From 300 K to 700 K, the collection efficiencies of both ash samples were as high as above 93%, but the collection efficiency of ash A in simulated gas decreased to 78.7% at 900 K.

Direct electrolysis of waste newspaper for sustainable hydrogen production: an oxygen-functionalized porous carbon anode

Biomass electrolysis enables hydrogen (H2) production at onset voltages of less than 1 V, depending on the fuel species. However, biofuel derived from biomass not categorized as food and produced from environmentally friendly processes is needed for the development of sustainable strategies. In addition, the biofuel should not require special and expensive procedures for processing. The present report describes the direct electrolysis of waste newspaper for H2 production. Cellulose and lignin included in the newspaper were subject to dissolution and hydrolysis in a phosphoric acid solvent at the anode in a temperature range of 100–175 °C. The resulting decomposition products were electrolyzed to H2 and carbon dioxide (CO2), at low onset voltages (ca. 0.2 V) and high current efficiencies (H2: 1.0, CO2: 0.9). Carbon black functionalized with carbonyl groups showed greater catalytic activity than a Pt/C catalyst for the anode reaction. H2 yield reached ca. 0.2 g per 1 g of newspaper in a batch cell. H2 was produced continuously in a current-density range of 0.15–0.25 A cm−2 while maintaining plateau-like voltage behavior in a flow cell. The energy consumed for electrolysis at a current density of 0.15 A cm−2 was as low as 1.27 kWh (Nm3)−1.

Photofield emission from SiGe nanoislands under green light illumination

Photofield emission from SiGe nanoislands formed by molecular beam epitaxy (MBE) have been investigated. Two types of nanoislands, namely the domes and pyramids with different heights, have been addressed. It was found that the arrays of SiGe nanoislands exhibited a low onset voltage for field emission. The increase of emission current and the decrease of the curve slope in Fowler-Nordheim coordinates under green light illumination have been revealed. Electron field emission and photoemission from SiGe nanoislands have been explained based on the energy band diagram of Si-Ge heterostructure and some energy barriers have been determined.