Silver Buffer Layer Research Articles

A Study on the Field Emission Characteristics of High-Quality Wrinkled Multilayer Graphene Cathodes.

Field emission (FE) necessitates cathode materials with low work function and high thermal and electrical conductivity and stability. To meet these requirements, we developed FE cathodes based on high-quality wrinkled multilayer graphene (MLG) prepared using the bubble-assisted chemical vapor deposition (B-CVD) method and investigated their emission characteristics. The result showed that MLG cathodes prepared using the spin-coating method exhibited a high field emission current density (~7.9 mA/cm2), indicating the excellent intrinsic emission performance of the MLG. However, the weak adhesion between the MLG and the substrate led to the poor stability of the cathode. Screen printing was employed to prepare the cathode to improve stability, and the influence of a silver buffer layer was explored on the cathode's performance. The results demonstrated that these cathodes exhibited better emission stability, and the silver buffer layer further enhanced the comprehensive field emission performance. The optimized cathode possesses low turn-on field strength (~1.5 V/μm), low threshold field strength (~2.65 V/μm), high current density (~10.5 mA/cm2), and good emission uniformity. Moreover, the cathode also exhibits excellent emission stability, with a current fluctuation of only 6.28% during a 4-h test at 1530 V.

Interfacial Passivation of Perovskite Solar Cells by Reactive Ion Scavengers

Lead halide perovskites suffer from uncontrolled ion migration and the interactions at the external contacts play a fundamental role in the hysteretic response and performance degradation kinetics. In this work, we passivate the external interfaces by a reaction of migrating iodide ions with a silver buffer layer placed between Spiro-OMeTAD and Au layers. In the presence of an electrical field, iodine migration occurs and ions that are close to the perovskite/contact interface irreversibly form a layer of AgI. Overall, the interfacial reaction of iodide ions totally suppresses hysteresis and leads to more stable devices. A new sample preparation method unburies the reactive interface, which is then probed by X-ray photoelectron spectroscopy measurements. The kinetics of the layer formation are monitored by impedance spectroscopy highlighting that in the presence of an electrical field and light, the reaction occurs in the order of minutes. We further identify the resistive response of AgI in operating devices. The present work provides a new approach to passivate the external interfaces in lead halide perovskites.

Enhanced field electron emission of single-walled carbon nanotubes prepared by imprinting technique

In this work, single-walled carbon nanotubes (SWCNTs) field electron emitters were fabricated by imprinting SWCNTs on substrates with a silver buffer layer. It was found that the field emission properties of imprinted SWCNTs were significantly improved with turn-on field at 0.62 V/μm and threshold field at 1.04 V/μm, comparing to screen-printed SWCNTs emitters who had turn-on field at 1 V/μm and threshold field at 2 V/μm. These improvements of SWCNTs emitters were owing to the directly imprinting method which made SWCNTs have clean surface and more emitters on the substrates. The lower turn-on electric field of field emission was attributed to no impurities encapsulate on the emitters and the large aspect ratio of SWCNTs resulting in high field enhancement factor of 15800. The emission performance of the imprinted cathode was almost unchanged after many times repeated experiments. This simple and low cost technique can fabricate high performance field emission cathodes efficiently and also demonstrates potential applications in many electronic devices.

Structural Properties of 300 Å of Iron Films Grown on Polycrystalline Substrate

In this manuscript, the structural properties such as the distance inter-reticular of samples is studied, In the fact, four samples were used symbolized as follows: E tAg(Å), the only difference is the thickness of the Silver buffer layer (tAg= 0, 50, 100 and 150 Å) to find out how the thickness of this layer depends on the structural characteristics of the Iron thin layer, all samples are deposited using molecular beam epitaxy (MBE) at room temperature onto Si (100) substrate. The structural properties of all samples examined using X-ray diffraction method at small and high angles. The small angles X-Ray diffraction curves confirmed to us that there is a clear difference between the surface structure of the samples by varying the number of Kiessig Fringes, Also high angles X-Ray diffraction curves assured us this difference through the clear variation in the angular positions of the peaks of Bragg and the distances inter-reticular values from a sample to the other.

(Invited) The Key Processing Issues and Their Solutions for High-Quality Perovskite Solar Cells

We report the fabrication of cesium-doped mixed cation perovskite solar cells (PSCs) (FTO/c-TiO2/mp-TiO2/Perovskite/spiro-OMeTAD/Au). A few key processing issues and their solutions are introduced. The smooth, shiny, and dark perovskite film is deposited by using the anti-solvent method through spin-coating. First, the deposition of a pinhole-free c-TiO2 layer with a smooth surface is critical. Here, we introduce a new TiO2 solution using titanium isopropoxide (TiO2 99.99%) to tackle the issue the issues related to the conventional TiO2 solutions. Compared to the conventional one, the spin-coating of the new solution provides a pinhole-free, efficient hole-blocking layer without cracks and still cheaper and quicker than the latter one. Highly reproducible PSCs with an average power conversion efficiency (PCE) of 15.4% are fabricated using this solution compared to the conventional solution utilizing both spin-coating and spray pyrolysis with average PCEs of 10.6% and 13.78%, respectively. The anti-solvent method was usually used with chlorobenzene (CBZ), but CBZ cannot dissolve the Li-TFSI particles which may be present on the surface of mp-TiO2 right after Li-doping process. In this case, we should use a solvent that can dissolve the Li-TFSI particles completely. Both diethyl ether (DEE) and the mixed of CBZ and DEE (volume ratio of 4:1) can dissolve the Li-TFSI particles easily. It improves the size of perovskite particles which leads to lower density of defects in the film compared to the one with smaller particles. The overall PCE is enhanced to 15.9% for samples with CBZ:DEE compared to the PCE of 14.76% for samples with CBZ in the same processing conditions. Moreover, a thin layer of silver (Ag) is introduced as the interlayer between the hole transport layer (HTL) and the Au. We deposited a 2-5nm of Ag on top of the HTL followed by 80 nm of Au. By this, the adhesion of the Au layer to the device is improved according to the simple tweezer tool test. A pure Au film can easily come off from the surface of the HTL, however, the Au films with 2-5nm of silver buffer layer show strong adhesion to the device. Interestingly, the employment of 2nm silver film improved the current density and, finally the PCE of the devices by both improving the adhesion of the back electrode onto the device and increasing the light reflection in the PSC. Finally, a reproducible fabrication procedure of PSCs with an average PCE of 16.5%, and a maximum PCE of 17.43% for an active area of 0.08 cm2 is achieved.

Magnetoelastic Properties of Epitaxially Grown Co2Fe0.4Mn0.6Si and Co2FeGa0.5Ge0.5Heusler Alloys Thin Films

The out-of-plane magnetocrystalline anisotropy and magnetoelastic properties of series of epitaxially grown layers of Co2Fe0.4Mn0.6Si (CFMS) and Co2FeGa0.5Ge0.5 (CFGG) Heusler alloys thin films deposited on MgO with chromium buffer layer were investigated by means of the ferromagnetic resonance (FMR), SQUID magnetometer, and by the strain modulated FMR technique. The magnitude of the magnetocrystalline anisotropy constant was found to decrease with increasing layer thickness. The change of the anisotropy is caused mainly by the surface effects. However, for some of the samples series, the change of chemical ordering with the change of the magnetic layer thickness was also observed. An additional silver buffer layer influence on the properties of the magnetic layer was also investigated. For all three of the investigated series of the Heusler alloys, i.e., CFMS without Ag, CFMS with Ag, and CFGG, the experimentally observed magnitude of the magnetoelastic constant increases with the increase of the magnetic layer thickness.

Characterization of thin-metal anode buffers in organic devices

The interposition of a thin-metal buffer between the anode and active layers of an organic light emitting diode (OLED) can significantly improve hole injection. Experimental results of devices using silver, gold, and gold-palladium layers are presented and correlated to their respective work functions. A significant reduction in resistivity was observed with a silver buffer layer in a bilayer OLED device. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2070–2072, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21837

Antiferromagnetic interlayer coupling in epitaxial Fe/EuS (100) bilayers (abstract)

We present the observation of antiferromagnetic interlayer coupling between two ferromagnetic layers of Fe(100) and EuS(100), which are in direct contact. The coupling strength J is about 0.2 mJ/m2 at 5 K, it decreases with increasing tempeature and becomes negligibly small near the Curie temperature of the EuS layer. The samples were molecular-beam epitaxy-grown on the GaAs(100) single crystal substrates using a silver buffer layer. The structural and chemical properties of the layers were characterized by in situ low-energy electron diffraction and Auger electron spectroscopy and by ex situ Rutherford backscattering. Superconducting quantum interference device (SQUID) magnetometry was used for measurements of the absolute magnetic moments as a function of temperature or magnetic field. Hysteresis measurements were performed by means of the magneto-optical Kerr effect (MOKE). We found evidence of antiferromagnetic coupling between the two different ferromagnetic layers both from zero field cooling experiments through Tc(EuS) as well as directly from the shape of the hysteresis loops at low temperatures. The temperature dependence of the interlayer coupling strength shows that J is proportional to the EuS magnetization. The observed onset temperature of ferromagnetic order in EuS is up to three times higher than the Curie temperature of bulk EuS. We discuss a mechanism in which this enhancement is connected to the existence of structural defects in the EuS film, caused by the growth. The defects produce additional band carriers, which in turn enhance the Curie temperature of the layer due to a very large indirect s(d)–f exchange.

Comparison of magnetic coupling between permalloy films separated by Cr for polycrystalline and epitaxially grown structures

Two series of magnetic multilayers consisting of two 600 /spl Aring/ permalloy (Ni/sub 83/Fe/sub 17/) layers separated by varying thicknesses of Cr, sandwiched between two further layers of Cr have been studied by spin wave resonance (SWR). One series of samples has polycrystalline layers, and for comparison a second series of epitaxial layers were grown on GaAs(100) substrates. The (100) epitaxy of the silver buffer layer with the GaAs(100), is followed by the (100) epitaxy of the Cr layer. A four domain (011) epitaxy for the permalloy is deduced from the symmetry of the Cr and permalloy layers. For the polycrystalline layers the magnetic coupling is observed to decrease monotonically to zero. The epitaxial layers show evidence of oscillatory exchange coupling; this is discussed with respect to its long period and interfacial roughness.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microstructure and magnetic anisotropy of ultrathin Co/Pt multilayers grown on GaAs (1̄1̄1̄) by molecular-beam epitaxy

Multilayers of (Co3 Å, Pt15 Å)x, x=15 or 30 repeats, with or without a 200 Å silver buffer layer, were grown on GaAs (111) substrates by molecular-beam epitaxy. Vibrating sample magnetometry measurements confirmed that the samples with the Ag buffer layer show strong uniaxial magnetic anisotropy perpendicular to the surface. The perpendicular anisotropy exhibited by these metallic superlattices is discussed in terms of the microstructure of the overall multilayer stack, as well as the structural characteristics of the Co interface layer. Samples grown on the Ag buffer layer show strong (111) texture with 30–40-nm-size twin-related grains. These grains, correspond to the two possible (111) stacking sequence for an fcc lattice, i.e., double positioning. However, direct growth on GaAs (111) results in randomly oriented 10–20 nm grains. All samples exhibit a repeat period of 1.83 nm in both low-angle reflectivity and high-angle Θ–2Θ x-ray scattering measurements. In addition, transverse scans through the low-angle multilayer Bragg peaks show the interfaces to be diffuse in nature indicative of considerable in-plane inhomogeneity and/or compound formation. High-resolution electron microscopy measurements of cross sections compared with image simulations confirm that the interface layer is diffuse and its stoichiometry is such that the Co occupation is less than 40%. Redistribution of Co should then extend over at least four monolayers. The nanostructure of the samples grown with the Ag buffer layer comprises an eight atomic layer repeat with the Co interface layer diffuse over four monolayers. The microstructure is strongly (111) textured with columns of twin related 30-nm-sized grains. It is suggested that the combination of interdiffusion, highly oriented but twin-related columnar growth, small grain size with a possible nanometer-scale second phase may be the key to the understanding of the perpendicular anisotropy observed in these (111) superlattices.

Superconducting Bi-Sr-Ca-Cu-O Films Prepared by the Screen Printing Technique

It has been found that both Y-Ba-Cu-0 and Bi-Sr-Ca-Cu-0 films get poisoned /1 to 31 when prepared on alumina substrates. The authors have reported in an earlier communication / 4 / that a silver buffer layer prevents the poisoning of Y-Ba-Cu-0 superconducting films prepared on alumina substrates. Now, in this note the preparation of Bi-Sr-Ca-Cu-0 superconducting thick films on alumina substrates with silver buffer layer by the screen printing technique is reported. This attempt has beep made since the film can be processed in a period of 5 to 6 h, which is considerably less than the duration required for processing pellets.

Microstructure and superconducting properties of Y-Ba-Cu-O films prepared by chemical spray pyrolysis

Y-Ba-Cu oxide superconducting films were prepared by spray pyrolysis on (100) MgO substrates and alumina coated with a silver buffer layer. Acetate, nitrate, and oxide precursors were used as starting materials. The optimum starting compounds have been assessed and the effectiveness of rapid thermal processing as a fabrication tool for annealing of highTc superconducting films has been established. The superconducting behavior was found to be strongly dependent on the type of the precursor used, on the method of heat treatment, and on the substrate material. The films show preferred orientation and good adherence to the substrate. Transport measurements indicated that the films exhibited a superconducting transition with an onset temperature between 83–93 K and ending between 52–74 K. The critical current density was found to be strongly dependent on film processing.

Role of a silver buffer layer on the superconducting Y-Ba-Cu-O films deposited by screen printing on alumina substrates

The characteristics of Y-Ba-Cu-O superconducting films, prepared on alumina substrates with an intermediate layer of thick film high-temperature silver paste, are studied. It is found that the critical current density of the film has improved, perhaps due to the prevention of interactions between alumina and the superconducting film by the intermediate layer.

Role of a silver buffer layer on the superconducting Y-Ba-Cu-O films deposited by screen printing on alumina substrates

Role of a silver buffer layer on the superconducting Y-Ba-Cu-O films deposited by screen printing on alumina substrates

High resolution patterning of high Tc superconducting thin films

Micron and sub-micron size microbridges have been patterned in high Tc films. The degradation of superconductivity caused by ion beam etching and subsequent processing was minimized by using a thin silver buffer layer. Lift-off technology and post-annealing gave narrow microbridges with good Josephson response.