Thin High Quality Research Articles

Achieving thin wall and high surface quality of magnesium alloy tubes in combined process of hollow sinking after die-less mandrel drawing

Dimensions and surface roughness of magnesium alloy tubes were evaluated to elucidate the flattening behavior of asperity on the outer surface and the optimal condition for achieving thin wall and high surface quality in the combined process of the hollow sinking after die-less mandrel drawing. ZM21 tubes were drawn using a die after die-less mandrel drawing. Dimensions and surface roughness were measured, and the stress state of the asperity during hollow sinking was evaluated using finite element and slab methods. The results indicated that in hollow sinking after die-less mandrel drawing when the speed ratio was large, both a thin wall and high inner and outer surface qualities can be achieved under low die reduction, where the outer surface roughness was the least, owing to relatively large die pressure and drawing stress. Additionally, enhancing the flattening of the asperity due to bulk plastic deformation in tension was difficult even if drawing stress increased when the speed ratio in die-less mandrel drawing was large. Therefore, when the speed ratio of the die-less mandrel drawing was large before hollow sinking, the largest outer surface flattening was achieved under low die reduction, wherein die pressure was large.

Descriptive model of the transition from superconducting to normal state in thin high quality YBaCuO films by nanosecond electrical pulses

A descriptive model of normal zone (N-zone) propagation during the pulsed transition from superconducting to normal state (S-N switching) in the YBaCuO thin films is proposed. The model should explain the unexpected film damage. An ideal propagation of the N-zone was simulated using a combination of sinus-like functions, representing an unstable border between superconducting and normal states (S-N border). Plane geometry of the S film causes the concentration of current and expelled magnetic field at the film edges, which allows us to consider the S-N border as a separate object. Three cases, when the S-N border has effective penetration depth (λeff) of 2.45, 1.64, and 1.155 μm widths with accordingly different critical current densities and impact of coherent jets, are considered. To define numerical values of the S-N switching parameters, earlier obtained experimental parameters were taken. It was shown that the ideal propagation is insufficient to explain the damaging process. Based on the scanning electron microscope (SEM) images of damaged films, it is concluded that coherent jets and other magnetic hydrodynamics phenomena exist in the real N-zone propagation. During the propagation, closed S and N areas form and then are contracted, resulting in round dark spots visible in the SEM images. The conservation of the trapped magnetic flux is manifested during this contraction. Numerical calculations of contracting processes show that circular currents at λeff reach the Ginzburg-Landau de-pairing current densities. This explains the unexpected irreversible damage of the high quality thin YBaCuO films after the flash S-N switching.

Plasma‐Enhanced Atomic Layer Deposition of Al2O3 on Graphene Using Monolayer hBN as Interfacial Layer

AbstractThe deposition of dielectric materials on graphene is one of the bottlenecks for unlocking the potential of graphene in electronic applications. The plasma enhanced atomic layer deposition of 10 nm thin high quality aluminum oxide (Al2O3) on graphene is demonstrated using a monolayer of hexagonal boron nitride (hBN) as protection layer. Raman spectroscopy is performed to analyze possible structural changes of the graphene lattice caused by the plasma deposition. The results show that a monolayer of hBN in combination with an optimized deposition process can effectively protect graphene from damage, while significant damage is observed without an hBN layer. Electrical characterization of double gated graphene field effect devices confirms that the graphene does not degrade during the plasma deposition of Al2O3. The leakage current densities are consistently below 1 pA µm−2 for electric fields across the insulators of up to 8 MV cm−1, with irreversible breakdown happening above. Such breakdown electric fields are typical for Al2O3 and can be seen as an indicator for high quality dielectric films.

Effects of JGB Additives on the Microstructures and Electrical Properties of Electroplated Copper Foil

Extremely thin film high quality copper foil is required to ensure high performance in electronics and slimness in secondary batteries. During the electroplating of copper foil, Janus Green B(JGB) and Collagen were introduced as additives to the electrolytes to study their effects. The structural and electrical properties of the electroplated copper foil were evaluated. When each additive was added individually, the potential was increased. Specifically, the potential of the group with 30 ppm added collagen was about 27% higher rather than the non-additive group. When Cl- ions and MPSA(3-mercapto-1-propane sulfonic acid) were added to the electrolytes without collagen and JGB, the surface roughness(Rz) increased by about 136% to 2.24 μm compared to the non-additive group. This was the highest value among all groups. However, a uniform layer with a surface roughness value below 0.3 μm was formed when less than 30 ppm and 10 ppm collagen and JGB were added, respectively, to the electrolyte. The direction of crystal growth with the JGB additives tended to go forward to the (220) direction, and the crystal size was reduced by 10~27% compared to the non-additive group. The addition of Collagen is necessary to reduce the difference in resistivity of the shiny layer and right matte layer. JGB additives were required to reduce the deviation in grain size. The results confirmed that the accelerators, inhibitors and leveler need to be properly added to form a copper plating layer with low surface roughness and to reduce differences in crystal texture of the shiny layer and right matte layer. Copper foil can be safely and uniformly deposited from electrolytes with JGB below 10 ppm and collagen below 30 ppm.

Design of Perovskite Thermally Co‐Evaporated Highly Efficient Mini‐Modules with High Geometrical Fill Factors

Perovskite solar cells (PSCs) have emerged as a promising technology for next‐generation photovoltaics thanks to their high power‐conversion‐efficiency (PCE). Scaling up PSCs using industrially compatible processes is a key requirement to make them suitable for a variety of applications. Herein, large‐area PSCs and perovskite solar modules (PSMs) are developed based on co‐evaporated MAPbI3 using optimized structures and active area designs to enhance PCEs and geometrical fill factors (GFFs). Small‐area co‐evaporated PSCs (0.16 cm2) achieve PCE over 19%. When the PSCs are scaled‐up, the thin films high quality allows them to maintain consistent Voc and Jsc, while their fill factors (FF), which depend on the substrate sheet resistance, are substantially compromised. However, PSCs with active areas from 1.4 to 7 cm2 show a substantially improved FF when rectangular designs with optimized length to width ratios are used. Reasoning these results in the PSM design with optimal subcell size and for specific dead areas, a 6.4 cm2 PSM is demonstrated with a record 18.4% PCE and a GFF of ≈91%. Combining the high uniformity of the co‐evaporation deposition with active areas design, it is possible to scale up 40 times the PSCs with PCE losses smaller than 0.7% (absolute value).

Characterization of aluminum oxide thin films obtained by chemical solution deposition and annealing for metal–insulator–metal dielectric capacitor applications

A novel chemical formulation is presented that enables the chemical solution deposition of aluminum hydroxide thin films, which transforms into aluminum oxide through subsequent annealing. The proposed method represents a faster and more economical alternative for aluminum oxide thin film deposition that can be used in metal-insulator-metal (MIM) dielectric capacitor applications. The film properties were studied in detail via X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and optical spectroscopy. It is demonstrated that the obtained thin films present high optical quality, low-crystalline domains, and oxygen vacancies. The films that were obtained for a 30 min deposition time show a suitable surface morphology and thickness, determined by atomic force microscopy and a cross-section from scanning electron microscopy, of a dielectric layer which was used to fabricate a MIM device. Using capacitance-voltage and current-voltage characterizations on that device, a low leakage current in the 10−4 A/cm2 range and a capacitance of 98 and 48 nF/cm2 were measured. These results indicate that, both aluminum hydroxide and aluminum oxide thin films have dielectric properties that are comparable to those of silicon oxide. Thus, the proposed method allows the deposition of gate dielectric films at low temperatures through a technically simple and scalable process.

Optical anisotropy of theJeff=1/2Mott insulatorSr2IrO4

We report the complex dielectric function along and perpendicular to the IrO2 planes in the layered perovskite Sr2IrO4 determined by spectroscopic ellipsometry in the spectral range from 12 meV to 6 eV. Thin high quality single crystals were stacked to measure the c-axis optical conductivity. In the phonon response we identified 10 infrared-active modes polarized within the basal plane and only four modes polarized along the c-axis, in full agreement with first-principle lattice dynamics calculations. We also observed a strong optical anisotropy in the near-infrared spectra arising from direct transitions between Ir 5d t2g Jeff = 1/2 and Jeff = 3/2 bands, which transition probability is highly suppressed for light polarized along the c-axis. The spectra are analyzed and discussed in terms of relativistic LSDA+U band structure calculations.

An Efficient and Cost-Effective Method for Preparing Transmission Electron Microscopy Samples from Powders.

The preparation of transmission electron microcopy (TEM) samples from powders with particle sizes larger than ~100 nm poses a challenge. The existing methods are complicated and expensive, or have a low probability of success. Herein, we report a modified methodology for preparation of TEM samples from powders, which is efficient, cost-effective, and easy to perform. This method involves mixing powders with an epoxy on a piece of weighing paper, curing the powder-epoxy mixture to form a bulk material, grinding the bulk to obtain a thin foil, punching TEM discs from the foil, dimpling the discs, and ion milling the dimpled discs to electron transparency. Compared with the well established and robust grinding-dimpling-ion-milling method for TEM sample preparation for bulk materials, our modified approach for preparing TEM samples from powders only requires two additional simple steps. In this article, step-by-step procedures for our methodology are described in detail, and important strategies to ensure success are elucidated. Our methodology has been applied successfully for preparing TEM samples with large thin areas and high quality for many different mechanically milled metallic powders.

Palaeogene sequences with sedimentary characteristics controlling the lacustrine oil shale of the Meihe Basin

As a case study, the Meihe Basin, a typical Cenozoic faulted basin, was divided into and identified as five three-order sequences by utilizing core, well logging, and seismic data, as well as palaeontological and geochemical data. Field measurements of sections, core observations, and a comprehensive analysis revealed that the basin is mainly composed of deposits of alluvial fan, fan delta, lacustrine facies, and gravity flows, and oil shale is mainly developed in semi-deep and deep lacustrine environments. The comprehensive study of the sediment-sequence stratigraphy indicates that Sequence I was formed in the initial rifting stage of the basin, dominated by coarse clastic sediments of alluvial fan and fan delta. Sequence II was formed in the rifting expansion stage of the basin, with more developed sediments of fan delta and lacustrine. Sequence III was formed in the largest expansion stage of the basin, dominated by mudstone of deep lacustrine facies and gravity flow deposits. Sequence IV was formed in the shrinking stage of the basin, dominated by sediments of delta and lacustrine fan. Oil shale are mainly developed in the transgressive system tract (TST) and highstand system tract (HST) of Sequence III (Mudstone Member of lacustrine facies). The lake flooding effect of TST can reduce the decomposition amount of organic matter, increase in organic matter production, and reduce the amount of dilution, thus forming oil shale with a thin consistency but high quality. In the period of the HST, the larger accommodation space and excellent organic matter preservation conditions are conducive to developing stable oil shale with a greater consistency. During the high water level period, however, due to the oxygen brought in by turbidites, the decomposition of organic matter is often increased, resulting in the formation of low-quality oil shale.

High-Voltage and Low-Leakage-Current Gate Recessed Normally-Off GaN MIS-HEMTs With Dual Gate Insulator Employing PEALD-${\rm SiN}_{x}$/RF-Sputtered-${\rm HfO}_{2}$

To fabricate gate recessed normally-off AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors, we have employed a novel SiNx/HfO2 dual gate insulator. A plasma enhanced atomic layer deposition (PEALD) technique was used for very thin high quality SiNx (5 nm) as an interfacial layer followed by RF-sputtered HfO2 as a high- k dielectric for the second gate insulator structure. The PEALD SiNx interfacial layer effectively suppresses the forward gate leakage current and the current collapse. We have achieved excellent characteristics such as large threshold voltage of 1.65 V, high breakdown voltage of 900 V, extremely small off-state drain leakage current less than 10-9 A/mm and high ON/OFF drain current ratio of ~ 109, low on-state resistance of 1.84 mΩ·cm2, and small subthreshold slope of 85 mV/decade.

Material-Selective Surface Chemistry for Nanoplasmonic Sensors: Optimizing Sensitivity and Controlling Binding to Local Hot Spots

Optical sensors utilizing the principle of localized surface plasmon resonance (LSPR) offer the advantage of a simple label-free mode of operation, but the sensitivity is typically limited to a very thin region close to the surface. In bioanalytical sensing applications, this can be a significant drawback, in particular since the surface needs to be coated with a recognition layer in order to ensure specific detection of target molecules. We show that the signal upon protein binding decreases dramatically with increasing thickness of the recognition layer, highlighting the need for thin high quality recognition layers compatible with LSPR sensors. The effect is particularly strong for structures that provide local hot spots with highly confined fields, such as in the gap between pairs of gold disks. While our results show a significant improvement in sensor response for pairs over single gold disks upon binding directly to the gold surface, disk pairs did not provide larger signal upon binding of proteins to a recognition layer (already for around 3 nm thin layers) located on the gold. Local plasmonic hot spots are however shown advantageous in combination with directed binding to the hot spots. This was demonstrated using a structure consisting of three surface materials (gold, titanium dioxide, and silicon dioxide) and a new protocol for material-selective surface chemistry of these three materials, which allows for controlled binding only in the gap between pairs of disks. Such a design increased the signal obtained per bound molecule by a factor of around four compared to binding to single disks.

200 mm Silicon On Porous Layer Substrates Made by the Smart Cut Technology for Double Layer-Transfer Applications

Silicon On Porous Layer (SOPL) substrate was fabricated by applying the Smart Cut technology to silicon substrate having a superficial porous Si layer. It consists in a non-porous/porous single crystalline Si bilayer transferred onto a handling wafer to form Silicon-On-Insulator (SOI) like structure. Subsequent bonding to a final wafer and separation induced in the fragile embedded porous Si layer led to the double transfer of the single crystalline non porous Si layer. Changes in structural and mechanical properties of the embedded porous silicon layer as a function of the annealing temperature were also determined. Thickness homogeneity of the transferred thin Si layer was estimated after SOPL fabrication and after double layer-transfer achievement. The perfect crystallinity of the active Si layer was conserved during the whole process. SOI-like structure fabrication and subsequent separation of thin high quality Si film are reported in order to demonstrate capability of SOPL structure with double-sided layer processing for device integration.

200 mm Silicon on Porous Layer Substrates Made by the Smart Cut Technology for Double Layer Transfer Applications

Silicon On Porous Layer (SOPL) substrate was elaborated by applying the Smart Cut{trade mark, serif} technology to silicon substrate having a superficial porous Si layer. Porous Si layer morphology was characterized after anodisation process. A single crystalline/porous Si bilayer was transferred onto a handling wafer to form SOI like structure. Subsequent bonding to a final wafer and separation induced in the fragile embedded porous Si layer led to the double-transfer of the single crystalline Si layer. Changes in mechanical properties and chemical composition of the embedded porous silicon layer as a function of the annealing temperature were also determined. Thickness homogeneity of the transferred thin Si layer was estimated after SOPL fabrication and after double-transfer achievement. The perfect crystallinity of the active Si layer was conserved during the whole process. SOI-like structure fabrication and subsequent separation of thin high quality Si film are reported in order to demonstrate adequacy of SOPL with post device post processing substrate removal.

Photoconductivity Measurements of Organic Polymer/Nanostructure Blends

AbstractIn an attempt to produce low cost and high quality polymer/nanoparticle blends for use in hybrid organic/inorganic photovoltaic devices we prepared blends of dihexylsexithiophene and tetragonal barium titanate particles. These polymer nanoparticle blends were deposited as films by spin coating and sublimation. The films were characterised and compared using a wide range of techniques; The electrical photoconductivity analysis of these structures carried out using an HP4140B picoammeter and a solar simulator after aluminium gap cell electrodes had been deposited on the films by sublimation, spectroscopic studies (FTIR and UV-VIS) were carried out to understand the photoconductivity measurements and ellipsometry was used to determine the thickness of the films. The photoconductivity of the spin coated films was the highest reaching 8.5x 10-10A at 20 V, the sublimed films reached ~4 x 10-10A at 40V. This is thought to be due to the thinness of the sublimed films combined with the inhomogeneous distribution of nanoparticles compared with the spin coated film. Sublimed films have been shown by others to be better structured than spin coated films, if this property can be utilized with further optimization of the sublimation process then this technique offers the potential to produce very thin high quality films for use in organic and hybrid photovoltaic devices.

Realization of Hybrid Silicon core/silicon Nitride Shell Nanodots by LPCVD for NVM Application

AbstractWe present the realization of hybrid silicon core/silicon nitride shell nanodots by Low Pressure Chemical Vapor Deposition (LPCVD) and their application as floating gate in Non Volatile Memory (NVM) devices. The LPCVD process includes three steps: nucleation using SiH4, selective growth of the silicon nuclei using SiH2Cl2 and finally selective growth of silicon nitride using a mixture of SiH2Cl2 and NH3 around the silicon dot. The two first steps have already been described in literature. We will therefore focus on the selective growth of a nitride layer on silicon dots. Morphological characterization using Scanning Electron Microscopy (SEM) allows control over dots size – 5 to 10nm – and density – up to 1E12/cm2. High Resolution Transmission Electron Microscopy (HRTEM) shows a crystalline silicon core and an outer shell of amorphous silicon nitride. Energy Filtered TEM pictures confirm that the nitride layer is deposited only around the silicon dots and not on the oxide. Oxidation resistance of the silicon nitride shell is also investigated. A 2nm thick silicon nitride layer is an efficient barrier to an oxidation at 800°C in dry oxygen for 5 minutes. We thus have a very thin high quality stoechiometric nitride layer. Such a high quality nitride film can only be achieved using in-situ deposition i.e. on an oxide-free silicon surface. Finally, hybrid Si/SiN nanodots are integrated in a single memory cell with high-K interpoly dielectric. Electrical results show large threshold voltage shift of 6V. The use of silicon nitride shells on the silicon dots has therefore two main advantages: it provides both oxidation resistance and charge storage enhancement.

Biased target deposition

The biased target deposition apparatus described herein uses a low energy ion source. The ions are generated at energies for which the sputter yield is negligible for typical construction materials, so that there is no need for expensive optics to focus the ions on the target. The bias of the target provides the energy for sputtering the target material, in addition to restricting the sputtering to the target. Using the biased target technique, copper films were deposited with an average resistivity of about 2.5 μΩ cm at a thickness of 1000 Å. This apparatus is well suited to the deposition of very thin (⩽1000 Å) high quality films, such as used in recent magnetoresistive devices. It is also well suited for use in compact and reliable multitarget systems to deposit such films.

Ultra thin high quality stack nitride/oxide gate dielectrics prepared by in-situ rapid thermal N 2O oxidation of NH 3-nitrided Si

In this paper, we report ultra thin high quality nitride/oxide gate dielectrics prepared by rapid thermal NH 3 nitridation of Si followed by in-situ N 2O oxidation (NH 3+H 2O process). These films show excellent interface properties, significant lower leakage current (∼10 2X), enhanced reliability, and superior boron diffusion barrier properties compared with SiO 2 of identical equivalent oxide thickness (Tox,eq).

Epitaxial Growth of Sb/Ge/Si(111) Studied by Photoelectron Diffraction

X-ray photoelectron diffraction is used to investigate the epitaxial growth of thin high quality Ge films on Si(111). Several Ge films have been prepared with varying coverages with and without Sb terminating the interface towards the vacuum. The measured photoelectron pattern for monolayer Ge films exhibits only intralayer diffraction maxima due to the double layers formed by the Ge diamond structure. For thicker films interlayer scattering between two adjacent layers can be observed as well.

High-resolution infrared study of the translational lattice modes in α-N2 single crystals

The analysis of the far infrared spectrum of thin high quality α-N2 single crystals as a function of temperature was carried out by high resolution Fourier-transform infrared spectroscopy. The bandwidths at T=8 K of the two translational modes, correlated to the two-phonon density of states, are considerably smaller than the Raman active modes. This result can be interpreted on the basis of a lower anharmonicity of the translations with respect to the librational modes. The α-N2 is the first molecular crystal where such difference is found. The evolution of the T(1)u linewidth was studied until the α-β phase transition. The relaxation of this mode is essentially dominated by fourth-order decay processes. The study of the frequency shifts of both infrared phonons allowed the contributions relative to different orders of the anharmonic potential to be separated. Finally a careful analysis of the relative intensities of the two phonons was carried out in the α phase.

Are the nonlocal effects really actual for the HTSC?

Recently a new trend in theoretical works has appeared whiclr claims that the nonlocal effects may be relevant for the HTSC, containing high-Jc weak links (twin boundaries, stacking faults etc.). In such weak links a new type of vortices—Abrikosov-Josephson (AJ) vortices—may arise and move freely along the defects, leading to dissipation. In the present work the first observation of a steep non-linear dependence of the surface resistance Rs of YBaCuO thin film and high quality ceramic on microwave magnetic field amplitude Hω, which is a unique feature for the dissipation due to the current-driven oscillation of AJ-vortex, is reported. At the same time the dependence Rs (Hω) is well described by the current-induced critical state model proposed by Sridliar Additional experiments which may help to distinguish between the two models are discussed.