High Emission Stability Research Articles

2.7 Å cryo-EM structure of vitrified M. musculus H-chain apoferritin from a compact 200 keV cryo-microscope.

Here we present the structure of mouse H-chain apoferritin at 2.7 Å (FSC = 0.143) solved by single particle cryogenic electron microscopy (cryo-EM) using a 200 kV device, the Thermo Fisher Glacios®. This is a compact, two-lens illumination system with a constant power objective lens, without any energy filters or aberration correctors, often thought of as a “screening cryo-microscope”. Coulomb potential maps reveal clear densities for main chain carbonyl oxygens, residue side chains (including alternative conformations) and bound solvent molecules. We used a quasi-crystallographic reciprocal space approach to fit model coordinates to the experimental cryo-EM map. We argue that the advantages offered by (a) the high electronic and mechanical stability of the microscope, (b) the high emission stability and low beam energy spread of the high brightness Field Emission Gun (X-FEG), (c) direct electron detection technology and (d) particle-based Contrast Transfer Function (CTF) refinement have contributed to achieving high resolution. Overall, we show that basic electron optical settings for automated cryo-electron microscopy imaging can be used to determine structures approaching atomic resolution.

Field emission characteristics of metal nanoparticle-coated carbon nanowalls

Metal nanoparticles are deposited on nitrogen-incorporated carbon nanowalls (CNWs) using Ag, Au, In, and Mg as metal species for enhancing field emission. Morphology, coverage, chemical composition, and crystallinity of the metal coatings on CNW surfaces are examined by varying nominal thickness of metals within 10 nm. The emission characteristics reveal that coating CNWs with any metal species lowers emission turn-on fields and thus increases emission efficiency. The inverse dependence of field enhancement factor and turn-on field upon nominal thickness of metals confirms that additional field amplification at metal nanoparticles governs emission efficiency regardless of work functions of the metals. The Ag-coated CNWs retain the highest current density for long-time emission at a constant applied field, while the non-coated CNWs have higher emission stability and a larger time constant of current degradation than the metal-coated ones.

Green emitting Ba1.5Lu1.5Al3.5Si1.5O12: Ce3+ phosphor with high thermal emission stability for warm WLEDs and FEDs

By hetero-valence substituting Ba2+-Si4+ for Lu3+-Al3+ pair in Lu3Al5O12: Ce3+, a new green phosphor Ba1.5Lu1.5Al3.5Si1.5O12: Ce3+ (BLAS: Ce3+) has been obtained. It crystallizes in garnet structure with space group Ia-3d (230). In the structure, Ba2+ ions are incorporated into both dodecahedral Lu3+ and octahedral Al3+ sites while Si4+ ions only occupy tetrahedral Al3+ sites. Under the blue light irradiation of 450 nm, an intense green light peaking at 520 nm was observed and the PL spectrum can be fitted in two Gaussian components, due to the crystal field splitting of Ce3+ 5d states under D2 symmetry constrains. The optical doping concentration of BLAS: Ce3+ is 6% mol, of which the IQE and EQE are 89.1% and 51.8%, respectively. Furthermore, this sample exhibits an extremely good thermal stability, i.e. the integrated emission intensity is still more than 90% of the initial intensity at 480 K. Then, a w-LED device was fabricated from this new green phosphor BLAS: Ce3+ and commercial red phosphor (Ca,Sr)AlSiN3: Eu2+, which shows a quite high color rendering (Ra = 88.2) and a relatively low color temperature 4772 K. Besides, the phosphor exhibits a stable chromaticity under different acceleration voltages. The phosphor may be promising material for the development of solid-state lighting and display systems.

Field emission properties of carbon nitride synthesized by microwave plasma chemical vapor deposition

Crystalline carbon nitride is expected to be an emitter with a long lifetime and high emission stability, because it is composed of carbon and nitrogen with high oxidation resistance and its sharp shape facilitates the occurrence of electron emission. The purpose of this paper is to clarify the field emission properties of crystalline carbon nitride. We studied the improvements in the field emission properties of carbon nitride after surface treatments. The carbon nitride was synthesized using microwave plasma chemical vapor deposition from a CH4-N2 gas system. Si substrates with different electrical properties (p- and n-type of 0.01 and 1500 Ω, respectively) were used. The carbon nitride on the 0.01 Ω n-type substrate showed the highest current density of approximately 0.25 mA/cm2. The maximum current densities of the carbon nitride on the n-type or p-type substrates were higher than those of the undoped type by decreasing the resistivity of the substrate. The threshold field (emission current observed in the minimum electric field) of the carbon nitride on n-type substrates was decreased by decreasing the substrate resistance. In the case of Au-coated deposits on an n-type Si substrate of 0.01 Ω, a threshold field was observed at approximately 1 V/μm. In addition, the electric field emission current density at 20 V/μm was 0.83 mA/cm2. The ultra-thin coatings of Au on the carbon nitride were effective in decreasing the threshold field and increasing the maximum current density. The Fowler-Nordheim plots of the carbon nitride with or without Au coatings formed a straight line, indicating that the Fowler-Nordheim theory perfectly fit the field emission behaviors of samples.

Dy/Sm doped Ca3Si2O4N2 phosphors with high thermal emission stability

Dy3+ and Sm3+ activated Ca3Si2O4N2 samples have been prepared by high temperature solid state reaction, and their luminescence properties were investigated. The excitation spectrum of Ca3Si2O4N2:0.02Dy3+ monitored at 576 nm has several strong peaks from 340 to 410 nm. Under 365 nm excitation, its emission spectrum exhibits a dominant peak located at about 576 nm with the Commission Internationale de l’Eclairage chromaticity coordinates of (0.395, 0.422) and the correlated color temperature of 3932 K. Sm3+ doped Ca3Si2O4N2 exhibits red emission originating from 4G5/2 to 6HJ (J = 5/2, 7/2, 9/2 and 11/2) transitions, and the charge transfer band of Sm3+ was observed at an unusually low energy of 4.29 eV. As the concentration of Sm3+ increases, the emission intensity of the electric-dipole transition becomes stronger than that of the magnetic-dipole transition, indicating that the local environment of Sm3+ ions becomes more asymmetric. With the increasing temperature, both Sm3+ and Dy3+ doped Ca3Si2O4N2 phosphors exhibit satisfactory thermal stabilities.

六角密排多迭层碳纳米管阴极的大电子发射电流和高电子发射稳定性

六角密排多迭层碳纳米管阴极的大电子发射电流和高电子发射稳定性

Luminescence properties of phosphate phosphors Ba3Gd1−x(PO4)3:xSm3+

A series of reddish orange phosphors Ba3Gd1−x(PO4)3:xSm3+ (x = 0.02, 0.04, …, 0.12) were prepared by the high-temperature solid–state reaction. X-ray powder diffraction (XRD) and diffuse reflectance and photoluminescence spectra were utilized to characterize the structure and spectral properties of the phosphors. The phosphors have strong absorption in the near-UV region. CIE chromaticity coordinates of the phosphors are located in the reddish orange region since the strongest emission band is around 598 nm and related to the 4G5/2 → 6H7/2 transition of Sm3+. Optimal concentration of Sm3+ in the phosphors is about 6.0 at%. The quantum yield of the Ba3Gd0.94(PO4)3:0.06Sm3+ under excitation at 403 nm is about 52.07%. Temperature dependent photoluminescence spectra of the Ba3Gd0.94(PO4)3:0.06Sm3+ were measured and the phosphor exhibits high thermal stability of emission. All the results show that the Ba3Gd(PO4)3:Sm3+ phosphor may be a potential red phosphor for near-UV based white LEDs.

M8MgSc(PO4)7:xDy3+ (M = Ca/Sr) Single-Phase Full-Color Phosphor with High Thermal Emission Stability.

Two series of phosphors of Ca8MgSc(PO4)7:Dy3+ and Sr8MgSc(PO4)7:Dy3+ single-phase white-emitting phosphors with high thermal emission stability are synthesized by the high-temperature solid-state reaction. The crystal structure, photoluminescence (PL), PL excitation (PLE), and thermal PL quenching spectra of Ca8MgSc(PO4)7:xDy3+ and Sr8MgSc(PO4)7:xDy3+ were investigated and compared in detail. Upon excitation at 387 nm, M8MgSc(PO4)7:xDy3+ (M = Ca/Sr) showed white emission centered at 480, 571, 660, and 754 nm. The white-emitting Dy-phosphor Ca8MgSc(PO4)7:Dy3+ (CMSP:Dy) had good terminal stability. The emission intensity of Ca8MgSc(PO4)7:Dy3+ still remained 95.2% of that at room temperature at 160 °C, and remained 77.3% at 300 °C under 387 nm excitation.

Luminescent properties of Eu3+-doped α-NaYF4 single crystal under NUV-excitation

This paper reports on successful synthesis of α-NaYF4 single crystal doped with Eu3+ at various concentrations by a modified Bridgman method. The crystal structure is characterized by means of X-ray diffraction. The absorption spectra, excitation spectra and emission spectra were measured to investigate the optical properties of the single crystals. An intense red emission located at 611 nm with long lifetime of 9.03 ms was observed in single crystal under the excitation of 394 nm light. It benefits from the low maximum phonon energy of α-NaYF4 single crystal matrix (390 cm−1). The CIE chromaticity coordinate of the α-NaYF4 single crystal doped Eu3+ in 4 mol% concentration was calculated (x = 0.6055, y = 0.388), which was close to the National Television Standard Committee standard values for red phosphor (x = 0.67, y = 0.33). All these spectral properties suggest that that this kind of fluoride crystal with high thermal stability and high efficiency of red emission may be used as potential red phosphors for optical devices.

New Y2BaAl4SiO12:Ce3+ yellow microcrystal-glass powder phosphor with high thermal emission stability

New Y2BaAl4SiO12:Ce3+ microcrystal-glass powder phosphor (emitting at 537 nm under 460 nm excitation) exhibits high thermal emission stability.

Extremely Stable Current Emission of P-Doped SiC Flexible Field Emitters.

Novel P-doped SiC flexible field emitters are developed on carbon fabric substrates, having both low Eto of 1.03-0.73 Vμm-1 up to high temperatures of 673 K, and extremely high current emission stability when subjected to different bending states, bending circle times as well as high temperatures (current emission fluctuations are typically in the range ±2.1%-3.4%).

Patterned growth of single-crystal 3, 4, 9, 10-perylenetetracarboxylic dianhydride nanowire arrays for field-emission and optoelectronic devices

3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) organic nanostructures possess extraordinary electronic and optoelectronic properties. However, it remains a challenge to achieve patterned growth of PTCDA nanowire (NW) arrays for integrated device applications. Here, we demonstrated the high-density, large-area, uniform, and cross-aligned growth of single-crystalline PTCDA NW arrays by using Au nanoparticles (NPs) as the growth templates. The high surface energy of Au NPs led to the cross-aligned growth of organic NWs, enabling the growth of PTCDA NW arrays with any desirable patterns by pre-patterning the Au films on a Si substrate. The PTCDA NW arrays as field emitters show good performance with a large emission current density and high emission stability. Furthermore, photodetectors based on PTCDA NW arrays were constructed via a simple in-situ growth approach, which exhibited high sensitivity to a wideband light ranging from 400–800 nm and surpassed the individual NW-based photodetectors in terms of higher photocurrent and faster response speed. Successful applications of PTCDA NW arrays in field emission and photodetectors show a great potential application of organic NW arrays in future efficient electronic and optoelectronic devices.

Modeling L-Band Brightness Temperature at Dome C in Antarctica and Comparison With SMOS Observations

Two electromagnetic models were used to simulate snow emission at L-band from in situ measurements of snow properties collected at Dome C in Antarctica. Two different approaches were used: one based on the radiative transfer theory and the other on the wave approach. The soil moisture ocean salinity (SMOS) satellite observations performed at 1.4 GHz (21 cm) were used to check the validity of these models. Model results based on the wave approach were in good agreement with SMOS observations, particularly for incidence angles lower than 55°. Comparisons suggest that the wave approach is more suitable to simulate brightness temperature at L-band than the transfer radiative theory, because interference between the layers of the snowpack is better taken into account. The model based on the wave approach was then used to investigate several L-band characteristics at Dome C. The emission e-folding depth, i.e., 67% of the signal, was estimated at 250 m, and 99% of the signal emanated from the top 900 m. L-band brightness temperature is only slightly affected by seasonal variations in surface temperature, confirming the high temporal stability of snow emission at low frequency. Sensitivity tests showed that good knowledge of density variability in the snowpack is essential for accurate simulations in L-band.

Stable electron field emission from carbon nanotubes emitter transferred on graphene films

Carbon nanotubes (CNTs) arrays grown by microwave plasma enhanced chemical vapor deposition (MPCVD) method was transferred onto the substrate covered with graphene layer obtained by thermal chemical vapor deposition (CVD) technology. The graphene buffer layer provides good electrical and thermal contact to the CNTs. The field emission characteristics of this hybrid structure were investigated in this study. Compared with the CNTs arrays directly grown on the silicon substrate, the hybrid emitter shows better field emission performance, such as high emission current and long-term emission stability. The presence of this graphene layer was shown to improve the field emission behavior of CNTs. This work provides an effective way to realize stable field emission from CNTs emitter and similar hybrid structures.

Formation of urchin-like CuO structure through thermal oxidation and its field-emission lighting application

Urchin-like CuO microstructures were formed using simple, template-free, one-step thermal oxidation of Cu solid microspheres in an air atmosphere at temperatures ranging from 350 to 500°C. The urchin-like CuO microstructure consists of crystalline CuO nanowires grown radially on the surface of the sphere, a shell layer of CuO a few micrometers in thickness, and a hollow core. Study of the formation mechanism revealed that during oxidation, the nanowires grow from the surface, and the diameter, length, and population density of the nanowires increase with the oxidation time. For a sample formed at 450°C for a dwell time of 24h, the average diameter, length, and population density of the nanowires were 44.0nm, 11.5μm, and 25nanowires/μm2, respectively. The novel urchin-like structure and high aspect ratio of the nanowires elicit unique properties. Study of the magnetic properties revealed that the urchin-like CuO is a semihard magnetic material with a coercive force of 135Oe. Studies on the field-emission characteristics of the material demonstrated that an urchin-like emitter had a low turn-on field of 2.94V/μm, a high field enhancement factor of 3715, a high luminance of 11,080cd/m2, an excellent emission uniformity of over 3.5×3.5cm2, and high emission stability during a 50-h test at a current density of 100μA/cm2.

Modification of polymer velvet cathode via metallic Mo coating for enhancement of high-current electron emission performances

The effect of surface Mo coating on the high-current electron emission performances for polymer velvet cathode has been investigated in a diode with A-K gap of 11.5 cm by the combination of time-resolved electrical diagnostic and temporal pressure variation. Compared with uncoated polymer velvet cathode under the single-pulsed emission mode, the Mo-coated one shows lower outgassing levels (∼0.40 Pa L), slower cathode plasma expansion velocity (∼2.30 cm/μs), and higher emission stability as evidences by the change in cathode current, temporal pressure variation, and diode perveance. Moreover, after Mo coating, the emission consistency of the polymer velvet cathode between two adjacent pulses is significantly improved in double-pulsed emission mode with ∼500 ns interval between two pulses, which further confirms the effectiveness of Mo coating for enhancement of electron emission performance of polymer velvet cathodes. These results should be of interest to the high-repetitive high-power microwave systems with cold cathodes.

Composite TiO<SUB>2</SUB> Film with Quantum Dots Fabricated Through a Sol–Gel Process

A novel strategy has been developed to fabricate composite TiO2 films with CdTe quantum dots (QDs). Aqueous CdTe QDs with green-, yellow-, and red-emitting were prepared using thioglycolic acid as a capping agent. The QDs revealed high photoluminescence (PL) efficiencies under optimal preparation conditions. TiO2 sol was obtained by the controlling hydrolysis of tetrabutyl titanate in ethanol with poly(vinyl pyrrolidone). Diethanolamine was added to prevent the QDs from PL quenching generated by surface defects. After embedding the QDs in composite TiO2 film, the PL intensity of the QDs decreased because of the excitation and recombination between the QDs and TiO2. The PL peak wavelength of the QDs in films revealed a slight blue shift compared with their initial ones. The blue shift degree of the PL peaks depended on the properties of the QDs. Red-emitting CdTe QDs revealed a small blue shift of 1 nm while green-emitting ones revealed a blue shift of 7 nm. This indicated red-emitting QDs with high stability against incorporation. Facile preparation and excellent properties including high PL brightness, multicolor emission, and high stability make these films important applications in various fields.

Characterizations of High Stability of Field Emission of ZnO Nanorods Synthesized by Thermal-Vapor Growth

Characterizations of High Stability of Field Emission of ZnO Nanorods Synthesized by Thermal-Vapor Growth

Characterizations of High Stability of Field Emission of ZnO Nanorods Synthesized by Thermal-Vapor Growth

In this paper, we present the synthesis and characteristics of high stability of field emission of ZnO nanorods grown on a ZnO seed-deposited Si substrate by thermal-vapor growth. ZnO and graphite powders were used as sources and O2 and N2 as process gases. It was found that the growth of nanorods was poor when they were synthesized under one of the following conditions: 1) synthesis temperature ≤800 °C; 2) ZnO/graphite weight ratio ≤3/7; 3) O2/N2 flow ratio ≥9/7. Nevertheless, nanoleaves developed when the synthesis temperature was higher than 1200 °C, and nanoneedles grew when the synthesis time was longer than 1.5 h. Homogeneous nanorods were grown at 1000 °C for 1 h with an O2/N2 flow ratio of 5/7 and a ZnO/graphite weight ratio of 7/3. Improving the crystalline property of nanorods increased their UV emission intensity and field-emission current. Nanorods with a high aspect ratio possessed a high field enhancement factor and low turn-on electric field, whereas the photoluminescence intensity of nanorods was less dependent on their aspect ratios. The emission current variation was less than 20% when the nanorods were examined under an electric field of 7.3 MV/m for 5 h.

Millimetre and submillimetre atmospheric performance at Dome C combining radiosoundings andatmsynthetic spectra

The reliability of astronomical observations at millimeter and sub-millimeter wavelengths closely depends on a low vertical content of water vapor as well as on high atmospheric emission stability. Although Concordia station at Dome C (Antarctica) enjoys good observing conditions in this atmospheric spectral windows, as shown by preliminary site-testing campaigns at different bands and in, not always, time overlapped periods, a dedicated instrument able to continuously determine atmospheric performance for a wide spectral range is not yet planned. In the absence of such measurements, in this paper we suggest a semi-empirical approach to perform an analysis of atmospheric transmission and emission at Dome C to compare the performance for 7 photometric bands ranging from 100 GHz to 2 THz. Radiosoundings data provided by the Routine Meteorological Observations (RMO) Research Project at Concordia station are corrected by temperature and humidity errors and dry biases and then employed to feed ATM (Atmospheric Transmission at Microwaves) code to generate synthetic spectra in the wide spectral range from 100 GHz to 2 THz. To quantify the atmospheric contribution in millimeter and sub-millimeter observations we are considering several photometric bands in which atmospheric quantities are integrated. The observational capabilities of this site at all the selected spectral bands are analyzed considering monthly averaged transmissions joined to the corresponding fluctuations. Transmission and pwv statistics at Dome C derived by our semi-empirical approach are consistent with previous works. It is evident the decreasing of the performance at high frequencies. We propose to introduce a new parameter to compare the quality of a site at different spectral bands, in terms of high transmission and emission stability, the Site Photometric Quality Factor.