Yb Layers Research Articles

Charge generation layer with Yb assistant interlayer for tandem organic light-emitting diodes

Tandem organic light-emitting diode (OLED) devices require an efficient charge generation layer (CGL) between two stacked OLED units. In this study, a CGL with an Yb assistant interlayer was fabricated and investigated. The optical transmittance and charge generation performances of the CGLs were analyzed with respect to the Yb thickness. The best result was obtained at a Yb thickness of 3 nm, at which both the electrical and optical properties exhibited optimal performances. The optical transmittance was greater than 90 %; this was superior to the performances using Ag and Al interlayers. The insertion of a 3-nm Yb layer reduced the threshold voltage from 18 to 6 V. Capacitance measurements revealed that the insertion of the Yb layer enhanced charge generation in the CGLs, reducing the threshold voltage and enhancing charge transport. The tandem OLED device fabricated using Bphen:Liq/Yb/MoO3/TAPC as a CGL exhibited a 1.92 × enhancement in the current efficiency, which is nearly twice the ideal value, compared to a single-unit device. Thus, Yb is a promising candidate for use as an assistant interlayer in CGLs for high-performance tandem OLED devices.

Stabilized Li-Rich Layered Oxide Cathode by a Spontaneously Formed Yb and Oxygen-Vacancy Rich Layer on the Surface.

Li-rich layered oxides (LLOs) are among the most promising cathode materials with high theoretical specific capacity (>250 mAh g-1 ). However, capacity decay and voltage hysteresis due tostructural degradation during cycling impede the commercial application of LLOs. Surface engineering and element doping are two methods widely applied tomitigate the structural degradation. Here, it is found that trace amount lanthanide element Yb doping can spontaneously form a surficial Yb-rich layer with high density of oxygen vacancy on the LLO-0.3% Yb (Li1.2 Mn0.54 Co0.13-x Ybx Ni0.13 O2 where x = 0.003) cathodes, which mitigating lattice oxygen loss and the non-preferred layered-to-spinel-to-rock salt tri-phase transition. Meanwhile, there are also some Yb ions doped into the lattice of LLO, which enhance the binding energy with oxygen and stabilize the lattice in grain interior during cycling. The dual effects of Yb doping greatly mitigate the structure degradation during cycling, and facilitate fast diffusion of lithium ions. As a result, the LLO-0.3% Yb sample achieves significantly improved cycling stability, with a capacity retention of 84.69% after 100 cycles at 0.2 C and 84.3% after 200 cycles at 1 C. These finding shighlight the promising rare element doping strategy that can have both surface engineering and doping effects in preparing LLO cathodes with high stability.

Structural and optical properties of Cu2Se/Yb/Cu2Se thin films

Abstract In this study, two stacked layers of Cu2Se are nanosandwiched with 50 nm thick Yb slab. The films which are prepared by the thermal evaporation technique under vacuum pressure of 10–5 mbar are examined by the X-ray diffraction, scanning electron microscopy, energy dispersion spectroscopy and optical spectrophotometry techniques. The cubic phase of Cu2Se exhibits lattice contraction which results in strained structure and reduction in grain size upon insertion of Yb between two layers of Cu2Se. The nanosandwiching of Yb layer does not influence the optical energy band gap but significantly altered the optical conductivity parameters. The optical conductivity parameters are determined by the help of Drude-Lorentz approach for the dielectric dispersion. Particularly, while the scattering time at femtosecond levels and the drift mobility values increases, the free hole density decreases via the nanosandwiching procedure. The drift mobility and plasmon frequency of Cu2Se reached values of 35.2 cm2/Vs and 9.85 GHz, respectively, by the Yb nanosandwiching. The enhancements in mobility and free carrier density values make the Cu2Se thin films more appropriate for optoelectronic applications.

Yerli ve Yabancı Ticari Kahverengi Yumurtacı Tavukların Serbest (Free-Range) Yetiştirme Sisteminde Verim Özelliklerinin Karşılaştırılması

Araştırma serbest sistem yumurta tavukçuluğunda kullanılacak uygun tavuk materyalini belirlemek üzere yürütülmüştür. Bu amaçla yerli kahverengi yumurtacı Atak-S genotipi ile YB kodu verilen yabancı kahverengi ticari yumurtacı genotip verim ve yumurta özellikleri bakımından karşılaştırılmıştır. Araştırmada her bir genotipten 150‘şer adet olmak üzere toplam 300 adet tavuk kullanılmıştır. Her genotip kendi arasında üç parsele ayrılmış ve her parselde 50 tavuk barındırılmıştır. Derin altlıklı yer sistemli kümes içerisinde birim alanda (m2) 5 tavuk yetiştirilirken, otlatma alanında ise tavuk başına 4 m2 alan ayrılmıştır. Aynı gün kuluçka çıkışı yapılmış olan yarkalar 16 haftalık yaşta özel bir firmadan temin edilmiştir. Araştırma 80 haftalık yaşa kadar sürdürülmüş olup bu süre zarfında verim ve yumurta kalite özellikleri tespit edilmiştir. Bu özelliklerden, %50 yumurta verim yaşı, yumurta ağırlığı, tavuk-gün yumurta verimi, tavuk-kümes yumurta verimi, yaşama gücü, ak indeksi, sarı indeksi, haugh birimi ve sarı rengi bakımından genotipler arasında farklılık bulunmamıştır. Buna karşın, 18-80. hafta canlı ağırlığı, yem tüketimi, yemden yararlanma oranı, şekil indeksi, kabuk kalınlığı, kabuk direnci, et-kan lekesi oranı ve kabuk rengi bakımından ise genotipler arasındaki farklılığın önemli olduğu tespit edilmiştir. Araştırmada, genotiplerden herhangi birisinin bütün özellikler bakımından öne çıkmadığı belirlenmiştir. Ancak, piyasa şartları dikkate alınarak yapılan ekonomik analiz sonuçları ve hayvan hassasiyetleri bakımından yapılan gözlemler neticesinde Atak-S genotipinin serbest sistem yumurta tavukçuluğuna daha uygun olduğu sonucuna varılmıştır.

Effective Schottky barrier lowering of Ni silicide/p-Si(100) using an ytterbium confinement structure for high performance n-type MOSFETs

A simple but effective rare earth metal (RE) confinement structure is demonstrated to suppress surface accumulation of Yb generally encountered in the RE metal incorporated Ni silicide system. The confinement structure is realized by inserting a Ti diffusion barrier layer between Yb and Ni layers. Yb atoms can be constrained in a specified reaction region during silicidation as evidenced by Auger electron spectroscopy and cross-section transmission electron microscopy analysis. The RE metal confinement structure provides a complementary metal-oxide-semiconductor compatible approach for further Schottky barrier height engineering and is a promising method for future technology nodes.

Performance of organic photovoltaics using an ytterbium trifluoride n-type buffer layer

Ytterbium trifluoride (YbF3) was used as an n-type cathode buffer layer in conventional poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PC60BM) bulk heterojunction (BHJ) organic photovoltaic cells. This buffer layer acts as an electron-transport layer and improves the open circuit voltage (V oc), power conversion efficiency (PCE), and interfacial durability of the device. The physical properties and performance of the device were studied using impedance spectroscopy, photocurrent measurements, ultraviolet photoelectron spectroscopy, and atomic force microscopy. The PCE reached to 3.2% with a 65% fill factor under 1 sun irradiation. The PCE decreased to half of its original value after 120 h at room temperature in air or 24 h at 70°C in air. Comparison with Yb and TiOx cathode buffer layers reveals that YbF3 has superior performance and longevity. These findings suggest that YbF3 has the potential to replace costly device encapsulation.

Optical and electrical performance of Yb/InSe interface

In this study a 300nm ytterbium transparent thin film is used as substrate to a 300nm thick InSe thin film. The optical transmittance, reflectance and absorbance of the glass/InSe and Yb/InSe films are measured and analyzed. The optical data allowed determining the effects of the Yb layer on the energy band gap, on the dielectric and on optical conductivity spectra. The band gap of the InSe films shrunk from 2.38/1.39 to 1.90/1.12eV upon Yb layer interfacing leading to a band offset of 0.48/0.27eV. On the other hand, the modeling of the optical conductivity in accordance with the Lorentz theory revealed a free carrier scattering time, carrier density and mobility of 0.225 (fs), 3.0×1019(cm−3) and 2.53cm2/Vs for the Yb/InSe interface, respectively. As these values seem to be promising for employing the Yb/InSe interface in thin film transistor technology, the current–voltage characteristics of Yb/InSe/C Schottky diode were recorded and analyzed. The electrical analysis revealed the removal of the tunneling channels by using Yb in place of Al. In addition, the “on/off” current ratios, the Schottky barrier height and the switching voltage of the Yb/InSe/C device are found to be 18.8, 0.76/0.60eV and 0.53V, respectively.

Field emitters made of the contacted ytterbium and carbon nanolayers

The operation of field emitters of a new type prepared from contacted nanolayers of ytterbium and carbon has been investigated. The performed calculations and experiments allowed to optimize the emission characteristics of the emitters. The calculations took into account the existence of a transition zone between the layers of Yb and C. Emission characteristics of the cathodes including up to 40 pairs of layers of carbon and ytterbium with optimum thicknesses of 5 and 2 nm respectively were measured. The created multilayered emitters provide the average emission current density over the surface of the emitter up to 10–20 A/cm2 and show promise for use in miniature electronic devices.

透明β-NaYF4∶Yb,Tm/PMMA纳米复合材料的制备及其光学性能

采用高温溶剂热法制备了一系列不同Yb3+掺杂浓度的上转换发光纳米粒子3-NaYF4∶Yb,Tm和核壳结构的β-NaYF4∶Yb,Tm@β-NaYF4∶ Yb纳米粒子.采用X射线衍射(XRD)、场发射扫描电镜(FESEM)、光致发光(PL)谱对材料的物相结构、形貌特征和发光性质进行了表征和研究,并特别研究了温度对材料发光性能的影响.结果表明:保持Tm3+浓度不变,随着Yb3+掺杂浓度的增加,β-NaYF4∶Yb,Tm的发光强度先增大后减小.当Yb3+掺杂摩尔分数为30％时,474 nm和645 nm处的发光强度达到最大值;当Yb3掺杂摩尔分数为50％时,450 nm和692 nm处的发光强度达到最大值.在β-NaYF4∶Yb(30％),Tm上包裹一层β-NaYF4∶Yb壳层后,其发光显著增强,随壳层Yb3+摩尔分数的增加,发光强度也是先增大后减小.当壳层Yb3+摩尔分数为10％时,核壳结构纳米粒子的发光强度达到最大值;当壳层Yb3+摩尔分数达到40％时,核壳结构纳米粒子的发光强度已经低于未包裹时.将样品进行热处理后,荧光增强.样品的发光强度随环境温度的升高,红光变弱,蓝光增强.采用原位聚合法将β-NaYF4∶Yb,Tm纳米粒子与PMMA制成复合材料后,仍能保持较好的透明度和发光强度.

Structural and optical properties of Yb-doped ZnO films deposited by magnetron reactive sputtering for photon conversion

Doping wide band gap semiconductors, such as ZnO, with trivalent rare earth (RE) ions is well known to enhance their optical activity. The present paper shows that high quality ZnO:Yb layers can be obtained by RF magnetron sputtering and that an efficient electronic transfer from ZnO to Yb+3 ions can be achieved. It is also shown that the rare earth is optically active at any deposition temperature and that its contribution to the photoluminescence (PL) is important even at very low concentrations. In particular, for samples deposited at low temperatures, the rare earth strongly enhances the photon conversion, yielding a total PL up to three times more intense. On the other hand, if the layers are exposed to temperatures above 200°C, either during deposition or upon post-deposition annealing, the presence of Yb quenches the total PL. Thermal annealing of the films at 700°C under Ar or O2 gas flow highly improves the PL of both ZnO and ZnO:Yb.

Engineering lattice matching, doping level, and optical properties of KY(WO4)2:Gd, Lu, Yb layers for a cladding-side-pumped channel waveguide laser

Single-crystalline KY1-x-y-zGdxLuyYbz(WO4)2 layers are grown onto undoped KY(WO4)2 substrates by liquid-phase epitaxy. The purpose of co-doping the KY(WO4)2 layer with suitable fractions of Gd3+ and Lu3+ is to achieve lattice-matched layers that allow us to engineer a high refractive-index contrast between waveguiding layer and substrate for obtaining tight optical mode confinement and simultaneously accommodate a large range of Yb3+ doping concentrations by replacing Lu3+ ions of similar ionic radius for a variety of optical amplifier or laser applications. Crack-free layers, up to a maximum lattice mismatch of ~0.08 %, are grown with systematic variations of Y3+, Gd3+, Lu3+, and Yb3+ concentrations, their refractive indices are measured at several wavelengths, and Sellmeier dispersion curves are derived. The influence of co-doping on the spectroscopy of Yb3+ is investigated. As evidenced by the experimental results, the lattice constants, refractive indices, and transition cross-sections of Yb3+ in these co-doped layers can be approximated with good accuracy by weighted averages of data from the pure compounds. The obtained information is exploited to fabricate a twofold refractive-index-engineered sample consisting of a highly Yb3+-doped tapered channel waveguide embedded in a passive planar waveguide, and a cladding-side-pumped channel waveguide laser is demonstrated.

Fabrication of NIR-Vis Upconversion YO1–xF1+2x:Ln (Ln = Yb, Er, Ho, and Tm) Crystal Layers by Flux Coating and Investigation of Growth Manner

High-quality upconversion YO1–xF1+2x:Ln (Ln = Yb, Er, Ho, and Tm) layers with good adhesion, comprising densely packed, plate-shaped idiomorphic crystals, were directly grown on stainless steel (SUS) substrates by flux coating. The LiNO3–KNO3 flux effectively promoted crystal growth. Additionally, the near-infrared-to-visible (NIR-vis) upconversion fluorescence properties of the YO1–xF1+2x:Ln crystal layers could be tuned by varying the type of dopant (Ln element). YO1–xF1+2x:Yb,Er, YO1–xF1+2x:Yb,Ho, and YO1–xF1+2x:Yb,Tm crystal layers showed red, green, and blue fluorescence, respectively, under 980 nm laser irradiation.

Ytterbium-doped fibers fabricated with atomic layer deposition method

We report on a new fabrication method of producing ytterbium doped fibers by atomic layer deposition (ALD) in combination with the conventional modified chemical vapor deposition (MCVD) technique. An MCVD soot-preform with a porous layer of SiO(2) is coated with layers of Yb(2)O(3) and Al(2)O(3) prior to sintering, using the gas-phase ALD method. An SEM/EDS material analysis study shows that the dopants successfully penetrate the full thickness of 320 µm of the soot layer. An Yb-doped fiber fabricated by this technique shows a background attenuation of 20 dB/km, a uniform longitudinal Yb-doping profile, and good laser characteristics with a slope efficiency of 80%. Furthermore, we present a comparison in terms of photodarkening between the MCVD-ALD fiber and a solution doped fiber, fabricated with the same MCVD recipe. The new MCVD-ALD fiber appears to be more photodarkening resistant.

Heavy quasiparticles formed in the ferromagnetic Yb layers in the Kondo helical magnet YbNi3Al9as revealed by specific-heat measurements

Heavy quasiparticles formed in the ferromagnetic Yb layers in the Kondo helical magnet YbNi<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>3</mml:mn></mml:msub></mml:math>Al<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>9</mml:mn></mml:msub></mml:math>as revealed by specific-heat measurements

Investigation of n-Type Pentacene Based MOS Diodes with Ultra-Thin Metal Interface Layer

In order to realize stable n-type characteristics of pentacene for applying to the organic complementary metal-oxide-semiconductor field-effect transistors (CMOS), we have fabricated pentacene based MOS diodes using ultra-thin Yb layer such as 0.5-3nm between gate insulator and pentacene. From the results of capacitance-voltage (C-V) measurements, excellent n-type C-V characteristics of the devices with 1 and 2nm-thick Yb were observed even though the devices were measured in air. These results suggested that the n-type semiconductor characteristics of pentacene are able to be improved by the thin Yb interfacial layer. Furthermore, the improved n-type characteristics of pentacene will enable the fabrication of flexible complementary logic circuits utilizing one kind organic semiconductor.

Structure, charge ordering and physical properties of Yb2Fe3O7

The structural and physical properties of the layered Yb2Fe3O7 have been extensively investigated. Transmission electron microscopy (TEM) observations at room temperature reveal the presence of diffuse zigzag-type streaks at 1/3(h h l) running along the c* axis direction, suggesting the presence of a charge ordered state with a shorter coherence length in comparison with that in Lu2Fe3O7. The measurements of magnetization demonstrate that the replacement of Lu3+ by the magnetic Yb3+ ion in this layered system could result in visible effects on the low-temperature magnetic properties: the ferrimagnetic phase transition temperature decreases and an additional magnetic anomaly possibly attributed to antiferromagnetic coupling between Yb and Fe layers appears at around 50 K. Analysis of the dielectric properties shows that the Yb2Fe3O7 material in general has a large dielectric constant of about 5000 at room temperature, and a broader relaxation time distribution in comparison with ErFe2O4.

Electronic structure of thin ytterbium layers on W(110): A photoemission study

In the present work we report on high-quality results of angle-resolved photoemission studies of thin Yb layers (1-3 ML thick) on a W(110) substrate. Growth of the thin Yb layers was monitored via permanent measurements of photoemission spectra during Yb deposition. This method allows to monitor the thickness of the deposited Yb with very high accuracy due to strong layer-dependent binding energy shifts of the Yb 4f emission. Contrasting to Ce/W(110) no hybridization of the 4f states with the own 6s-derived band is observed for the Yb-layers. Instead, a splitting of the Yb 4f7=2 emission is observed around the -point that is due to interactions with the W 5 d-derived substrate band and could quantitatively be described in the framework of the Periodic Anderson model.

Electronic structure of thin ytterbium layers on W(110)

In the present contribution we report on the results of the angle-resolved photoemission (PE) studies of thin layers of Yb (1–3 ML-thick) on W(110) surface. The clear splitting of the Yb 4f7/2 state was observed in the PE spectra measured around γ̄ point for 1 ML-thick Yb film. The measured PE spectra were analyzed by means of the simplified periodic Anderson model.

Growth and characterization of Yb 3+ doped Y 2SiO 5 layers on Y 2SiO 5 substrate for laser applications

We report on the epitaxial growth and spectroscopic study of highly doped Y 2SiO 5:Yb 3+ (YSO:Yb) thin films on YSO substrates. The realization of Ge, La and Gd-codoped high quality thin films, with thickness up to 100 μm, is demonstrated. YSO:Yb layers have their fluorescence and absorption spectra similar to the bulk ones, with a globally higher crystalline quality. The Yb 3+ lifetime evolution exhibits a particularly slow decrease with Yb doping, proof of a low extrinsic quenching centers concentration. The refractive index increase with respect to dopants concentration is measured, and a phenomenological law is proposed. Such highly doped YSO:Yb layers could be an interesting alternative for active integrated optics or laser devices.

Ce and Yb doped InP layers grown for radiation detection

AbstractInP single crystals were grown by liquid phase epitaxy on semi‐insulating InP:Fe substrate with cerium (Ce) and ytterbium (Yb) additions to the growth melt. Grown layers were characterised by Hall measurements and low temperature photoluminescence spectroscopy. Both types of layers exhibit the change of electrical conductivity from n to p type. Ce and Yb have been found to be incorporated into the InP lattice since a sharp luminescence lines arising from inner shell transitions of Yb3+ and Ce3+ were detected at 1002 and 3534 nm, respectively. A metastable conductivity state of InP:Ce layers has been found at temperatures below 35 K, a phenomenon previously reported for InP:Yb layers. Similar electrical behaviour of InP (Ce, Yb) layers leads us to conclude that Ce acts as dominant acceptor impurity responsible for n→p conductivity change. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)