Recent research efforts have unlocked substantial improvements in the performance and reliability of InAs quantum dot lasers on silicon by mitigating the effects of active-region-adjacent misfit dislocations through the introduction of defect trapping layers (TLs). These TLs enable lifetimes of lasers on silicon comparable with those grown on native GaAs substrates. Even so, current state-of-the-art lifetimes still fall somewhat short of requirements for more widespread adoption as both types of lasers exhibit gradual degradation in performance with aging. In this work, we demonstrate that this gradual degradation is a result of the generation of point defect populations during aging, which, over time, coalesce into dislocation microloops which we characterize using scanning transmission electron microscopy (STEM). We selected a single high-performing laser from each of three large aging sets of QD lasers (1) on silicon with TLs, (2) on silicon without TLs (no-TL)), and (3) on native GaAs. Each selected device was aged for between 8700 and 12,000 h at 80 °C at a current density between 1050 and 1900 A cm-2, depending on the initial threshold current and output power. After 2700 h, the no-TL device had doubled its initial threshold current (a common metric for device failure), and after 5700 h it failed to lase entirely. The TL device and the GaAs device, however, show threshold current increases of just 35% and 46% respectively after 8700 h with extrapolated lifetimes of 45,000 h and 75,000 h. Note, however, that these numbers are not directly comparable due to somewhat harsher aging conditions for the GaAs device. After aging, the devices were imaged using backside electroluminescence to check for signs of inhomogeneous degradation. For all lasers, degradation appeared largely homogeneous aside from dark line defects associated with misfit dislocations in the devices on silicon. There are also regions of decreased luminescence throughout the structure for the two devices on silicon, which we attribute to misfit dislocations lying parallel to the laser ridge for the no-TL device and to misfit dislocations escaped from the TL for the TL device, as confirmed by plan-view STEM of these regions. With sufficient thinning of the plan-view foils, dislocation microloops with diameters ranging from 5 to 20 nm are visible both in the [001] zone imaging condition overlaid with the QD contrast and more clearly in various g-3g STEM weak beam imaging modes where competing QD contrast is minimized. In the no-TL device in regions within 100-150 nm of the heavily climbed misfit dislocations, there is a dramatic increase in loop density on the order of 1010 cm-2. We believe this to be the result of a large density of point defects expelled by the misfit dislocations as they undergo climb. Thus, degradation caused by climbing misfit dislocations is multifold: first an increase in total misfit length and second the generation of a high density of point defects which coalesce into microloop defects surrounding the misfit dislocation, all of which substantially enhance non-radiative recombination processes. Meanwhile, the TL and GaAs device active regions, though largely or entirely free of climbed misfit dislocations, are still observed to contain microloop densities on the order of 108–109 cm-2, which likely accounts for the gradual, homogeneous degradation observed in these devices. These microloops coalesce from elevated point defect populations in the active region, and while there are many remaining questions, such as whether these point defects are pre-existing or are generated during aging, this work points the way for future routes to improve device and material quality.

Gradual Degradation via Dislocation Microloop Formation in InAs Quantum Dot Lasers on Si and GaAs

Diffusive memristors, also known as volatile electrochemical metallization memory cells (ECMs), are recognized as extremely interesting devices for various applications in emerging memories and neuromorphic computing areas. For non-volatile ECM cells, it has been shown that the counter-electrode (CE) material plays a crucial role in the switching process by affecting the reactions at the CE/electrolyte interface. This is due to the different electrocatalytic activity of the CE material towards reduction-oxidation reactions, which determines the metal ion concentration in the electrolyte and ultimately impacts the switching kinetics. In this work, we look at the switching behavior of diffusive memristors and how this is affected by different CE materials with a special focus on (i) the understanding of the influence of the CE material on the volatile switching process of diffusive memristors and (ii) device engineering and optimization towards industrially used and CMOS-compatible materials. To that end, we used inert Pt metal and two non-noble metals widely used in semiconductor technology, namely, W and TiN, as CE materials in Ag/HfO2/CE-based diffusive memristor cells. Rectangular voltage pulses of different amplitudes were applied and the SET times were analyzed from the transient curves. The results show that the CE material has a significant effect on the SET kinetics, with interesting differences being observed depending on the voltage regime. It is found that non-noble CE materials such as TiN and W form a native oxide either during ambient transfer or during the ALD process of the HfO2 electrolyte film. This has been confirmed by the XPS analysis of different stacks with and without the HfO2 layer. Furthermore, the formation of interfacial oxides at the CE/electrolyte interface in the case of non-noble metals is also discussed in relation to the observed differences in the SET kinetics. The findings of this work highlight the significant role of the CE material in the switching process of Ag/HfO2-based diffusive memristors and the importance of considering interfacial oxide formation in the design of these devices. This work was in part funded by the German Research Foundation (DFG) under Grant No. SFB 917, in part by the Federal Ministry of Education and Research (BMBF, Germany) in the project NEUROTEC (Project No. 16ME0398K) and NeuroSys (Project No. 03ZU1106AB) and are based on the Jülich Aachen Research Alliance (JARA-FIT).

Effect of the Counter Electrode Material on the SET Kinetics of Ag/HfO2-Based Diffusive Memristors

Two-dimensional (2D) transition metal dichalcogenides (MX2, with M being a transition metal and X a chalcogen) have potential application in next-generation optoelectronics, electronics, chemical sensing and quantum technologies. Epitaxial growth of single crystal TMD monolayers at the wafer-scale is of significant interest for device applications. Metalorganic chemical vapor deposition (MOCVD) is a promising approach for TMD growth as it enables the use of high substrate temperatures (900-1000oC) and chalcogen/metal ratios (103-105) which are beneficial for epitaxy. In addition, the flow rate of precursors can be modulated during growth to enhance the surface diffusion of metal-containing species and control the lateral growth rate of TMD domains. Sapphire has emerged as a promising substrate for wafer-scale TMD monolayers and few layer films due to its crystallographic compatibility and commercial availability. Despite the broad interest in wafer-scale 2D TMDs, the fundamental understanding of how the growth conditions, e.g. growth temperature, impacts the epitaxial growth and properties of 2D TMDs has rarely been investigated. In this study, MOCVD growth of wafer scale MoS2 monolayer was carried out in a horizontal cold-wall reactor that includes an induction-heated rotating SiC-coated graphite susceptor and separate gas inlets for the metal and chalcogen precursors. Molybdenum hexacarbonyl (Mo(CO)6) and hydrogen sulfide (H2S) were used as precursors in a H2 carrier gas. A 2” c-plane sapphire substate was used for all MoS2 growths. The growth temperature was varied as 900oC, 950oC, and 1000oC. The flow rate of the molybdenum precursor used in this work ranged from 0.001 to 0.003sccm while the H2S flow rate was maintained at 400 sccm. Growths were carried out with a moderate reactor pressure of 50 Torr using H2 as the carrier gas. Using these conditions, growth of fully coalesced monolayer MoS2 was achieved in 10-30 minutes across the 2” substrate. AFM and FESEM were used to characterize the surface coverage and morphology of the layers and in-plane X-ray diffraction was used to assess the epitaxial quality. Spatially resolved Raman and photoluminescence spectroscopy were carried out to assess the uniformity of the monolayer and along with variable temperature photoluminescence measurements. A coalesced monolayer of MoS2 was achieved on 2” c-plane sapphire over the temperature range from 900oC to 1000oC. The surface coverage (growth rate) was found to be only weakly dependent on the growth temperature and scaled roughly linearly with Mo(CO)6 flow rate indicating that the growth is limited by mass transport rather than reaction kinetics. In-plane XRD phi-scans confirm that the films are epitaxially oriented with respect to the sapphire over the temperature range (900oC to 1000oC) with the (1120) of MoS2 aligned with the (1120) of α-Al2O3. The FWHM of the phi-scan peak of MoS2 decreases with increasing growth temperature, indicating a reduction in in-plane rotational misorientation of the MoS2 domains at higher growth temperature. The MoS2 monolayer sample grown at 1000oC exhibits strong photoluminescence at room temperature centered around 1.9 eV and defect-related emission which dominates at low temperature of 6 K. PL measurements also reveal an increase in the intensity ratio of the A exciton to trion emission with increasing growth temperature indicating a reduction in defects. Additional results correlating the structural and optical properties of the MoS2 monolayers to the transport properties of field-effect devices will be reported. The results of this work provide a deeper understanding of the epitaxial growth of MoS2 monolayers grown by MOCVD and the impact of defects on the optical and electrical properties of the layers.

Effects of Growth Temperature on the Properties of Wafer-Scale Epitaxial MoS2 Monolayers Grown by Metalorganic Chemical Vapor Deposition

This abstract explores the possibility of employing metal additive microfabrication of system in package (SiP) with inbuilt heat sinks and leadframe consisting of multiple pads for QFN packaging. The SiPs were fabricated using 17-4Ph stainless steel powder employing a relatively less expensive DMLS system. The use of affordable metal additive manufacturing systems is considered by the authors to encourage further research on its applicability towards heterogenous integration in the semiconductor industries. The International Technology Roadmap for Semiconductors (IRTD) 2012 emphasized on the importance of integration of system on chip (SoC) and SiP. DMLS is one possibility for such heterogenous integration due to the possibility of customization as the parts are directly fabricated from a CAD file. DMLS has been considered superior to its plastic or resin-based counterparts in applications where conductive parts with better accuracy and strength are required. All these features make DMLS parts, a possible option for the fabrication of SiP with few functionalities like heat sinks and connectivity. 3D packaging and heat extraction for die is one of the grand challenges of International Roadmap for Devices and Systems (IRDS). In this abstract, different QFN leadframes with and without cooling systems are presented. The original leadframe design with only the pads forms a comparison reference for the remaining three systems. The three systems are: QFN leadframe with microchannel, inlet, and outlet for fluid flow, QFN leadframe with arrays of fins below the die location, and a QFN leadframe with fins along with additional inlet and outlet for optional fluid flow. Figure 1 shows the CAD top views of all four proposed package system. Each package system can hold a 1cm by 1cm semiconductor die for testing purposes. The microchannels are 500um square channels whereas the fins are 1000um in diameter. The affordability comes with the trade-off of resolution and the present DMLS system can faithfully produce the mentioned dimensions with compatible features for the channels and fins. The first step towards the fabrication of the packages is the CAD design and simulation. The CAD design was then fed to the metal 3D printer, which then sliced the model and created 3D laser part. The fabrication proceeds by melting and fusing a 30um layer of powder, repeating the process, creating layers on top of layers, and fusing them together until the final 3D part is built as per the CAD file. EDM wire cutting or grinding of previously created support structure could be used to separate the parts from the build plate. Figure 2 shows the steps involved in fabrication. On each separate parts, 1cm by 1cm semiconductor dies (all same) are carefully placed. Wire bonding will be used to connect the via to the leadframe pads and inlets/outlets will be extended. The whole system will then be covered with epoxy and left to cure. The final step will be to grind away the back end of the cured part to remove support metal plate on the bottom of the packaging parts as shown in Figure 3. Figure 4 shows the separated parts with a spot for semiconductor die to be affixed and various other sub-parts. Figure 5 shows the water (colored for visibility) filled leadframe with microchannel, and the other one with fins, inlet, and outlet is shown in Figure 6. Figure 7 shows the preliminary infra-red image of all four devices heated to 40°C and left to cool down. The devices were in the same order as Figure 4. As per the theoretical idea, fins with channels performs the best followed by the one with microchannel, and the one with only fins based on the time required for them to cool down (a-f in Figure 4). The preliminary result appears promising and the material characterization along with testing is in process. Figure 8 and 9 shows the SEM characterization of build device compared to the design. The variation from the design is very small.

Additive Microfabrication of System in Package for Heterogenous Integration with Semiconductor Dies

It was both theoretically and experimentally proved that the growth of In Ga 4-xN quantum wells (QWs) on In Ga,_ N underlayer (x > y) would significantly improve the light emitting diodes (LEDs) performance, attributing to the reduction of non-radiative recombination centers, the decline of the internal electrostatic field, and the improvement of indium composition uniformity in QWs. Moreover, the reduced lattice mismatch between QWs and underlayer greatly suppresses composition pulling effect, which improves indium incorporation rate grown at the same temperature, resulting in In-rich InGaN with highly crystalline. However, to serve as templates for red emission QWs, a thicker InGaN pseudo-substrate with closer indium mole fraction to QWs grown beyond the critical layer thickness is desired. In this work, we present an approach to achieve a sub-micron size InGaN underlayer with high to 30 % indium composition, while the thickness is around 90 nm, far exceeding the critical layer thickness of such In-rich InGaN layer on planar c-plane GaN (reported less than 5 nm). The InGaN platelet is demonstrated by selective area growth (SAG) on arrays of GaN seed from circle openings with a diameter of 400 nm ina SiN, mask. To our best knowledge, SAG of InGaN results in random nucleation and uneven shape due to the low diffusion length of gallium precursor at relatively low growth temperature. It was reported that the selectivity of InGaN can be enhanced by introducing pyramid shaped GaN seed first, resulting in InGaN pyramid. However, the local indium composition fluctuation on the semipolar facet of the InGaN pyramid hinders pure red emission of QWs with small full width at half maximum (FWHM). In this work, planar hexagonal shape of GaN seed was introduced first before SAG of InGaN, leading to the formation of uniform InGaN platelets with c-plane domain morphology. The optical properties of the InGaN platelets were characterized by photoluminescence (PL, excited by a He-Cd laser of 325 nm, 15 mW, room-temperature), showing PL peaks around 530 nm with FWHM of 141 meV, suggesting around 30 % indium incorporated. AFM scan of the top c-plane surface of the InGaN platelet indicates an atomically flat surface without v-pits or trench defects while the thickness is over 90 nm. Cross-sectional TEM characterization of InGaN platelet suggests homogenous crystalline and shape interface between InGaN and GaN seed. According to localized EDX line measurements recorded with the same area, the InGaN platelet shows indium composition almost linearly increased from InGaN/GaN interface to c-plane surface. Detailed line profiles show indium composition of 25 % to 30 % at the top surface and 15 % to 20 % at InNGaN/GaN interface. Such high indium-content InGaN platelets are competitive candidates for the development of high-quality yellow-to-red emission InGaN micro-LED, by increasing the indium incorporation rate and reducing the lattice mismatch for later Inrich quantum wells.

High In-Content InGaN Platelets as Underlayer for Light-Emitting Diodes Toward Long Wavelength Application

The role of band-tail states (BTS) on the operation of |GZO TFTs is well established, however there is wide variation in the interpretation of the interaction and/or independence of channel mobility and charge trapping. In many reports the influence of BTS on the level of free charge is accounted for by an effective mobility which is dependent on the applied gate bias. While this may accurately match current-voltage characteristics, this treatment is lumping together the effects of charge trapping and carrier scattering which should remain distinct. When these effects are combined, a model which can accurately represent device behavior over a wide temperature range is not possible due to fundamental differences in temperature dependence. Bottom-gate TFTs were fabricated with a 50 nm IGZO film sandwiched between a 50 nm gate oxide and a 50 nm passivation oxide layer. The working metal was molybdenum for the gate electrode and source/drain contacts. A passivation anneal was done and a capping layer was added to promote electrical stability; full process details are provided in a previous report. Devices were tested using a Lakeshore cryogenic probe station, with transfer characteristic measurements taken from room temperature to below 100 K. Electrical measurements made on long-channel devices (L = 12 um) has revealed temperature-dependent behavior that is not explained by existing TCAD models employed for defect states and carrier mobility. An |GZO TFT device model has been recently developed using Silvaco Atlas, which accounts for the role of donor-like oxygen vacancy defects, acceptor-like BTS, acceptor-like interface traps, and a temperature-dependent intrinsic channel mobility. The model demonstrates a remarkable match to transfer characteristics measured at T = 150 K to room temperature. The temperature-dependent mobility follows a power-law relationship, resembling behavior consistent with ionized defect scattering. The mobility model is independent of carrier concentration, without dependence on the applied gate bias. Details of the material and device model, and associated defect distribution parameters will be presented.

Separation of Defect States and Intrinsic Channel Mobility on the Electrical Operation of IGZO TFTs

III nitride semiconductors have recently disrupted several industries and have remarkable potential to address unmet needs in electronics and optoelectronics. While gallium nitride (GaN) is the champion nitride material in solid state lighting and high power and high frequency electronics, there is abundant untapped potential in other nitrides that are otherwise harder to grow and to gain control over their electronic properties. Among these, Indium nitride (InN) that promises the highest saturation velocity in the nitride group poses two difficult challenges to realize its potential: (1) The epitaxial growth of high-quality InN films or structures is very challenging due to the competitive decomposition of InN at the temperatures for which efficient cracking of nitrogen sources occur, and (2) the difficulty in growing a larger bandgap barrier layer at the surface which requires even higher temperatures than the InN decomposition temperature, and with the absence of such layer, surface Fermi energy pinning challenges the modulation of the electron charge density to make functional transistor devices from any grown InN layers. Yes, there has been outstanding progress in the growth of InN layers by molecular beam epitaxy or plasma assisted metalorganic chemical vapor deposition (MOCVD), but the growth of smooth InN surfaces and the growth of larger barrier layers on InN has not been accomplished before: This work demonstrates by standard pulsed MOCVD growth the ability to grow defect free InN structures with smooth surfaces and the ability to grow with control GaN barrier layers and to demonstrate excellent transport characteristics in these structures. We hypothesized that coalescence of InN islands in constrained geometries such as lateral Fins can accelerate the formation of void-free and defect free InN growth within the first few nanometers of grown InN. We further hypothesized that we can raise the effective V/III ratio by pulsing the tri-methyl-indium source to avoid droplet formation, ripening and segregation which otherwise leads to the growth of defective and porous InN layers. We validated these hypotheses by studying growth parameters and Fin widths in the range of 60 nm to 2000 nm (and control planar samples) and demonstrated InN Fins with defect-free surfaces and single crystal structures. Unannealed Ti/Au metal contacts on packed InN Fin arrays resulted in effective (un-corrected) specific contact resistance of approximately 6Q¢um, which is much smaller than that obtained for current GaN ohmic contacts, with an extracted contact transfer length less than 1pm. To leverage these structures for high electron mobility applications and un-pin their surface Fermi energy, we successfully grew in-situ GaN/InN heterostructure without compromising the smooth InN surface. Transmission electron Microscopy showed clear interface between GaN and InN and single crystal structure. We then demonstrated that GaN can be selectively etched in the source/drain regions of the heterostructure and that unannealed Ti/Au metal contacts retain their low specific contact resistance on these structures. We are now investigating the fabrication of GaN/InN and AIN/INN HEMTs and their DC/RF performance.

Demonstration of Single Crystal InN & GaN/InN Heterostructures by MOCVD

The heterogeneous integration of IIl-nitride materials with other semiconductor systems for electronic devices is attractive because it combines the excellent electrical properties of the Ill-nitrides with other device platforms. Pursuing integration through metalorganic chemical vapor deposition (MOCVD) is desirable because of the scalability of the technique, but the high temperatures required for the MOCVD growth of Ill-nitrides (>1000 °C) are incompatible with heteroepitaxy on some semiconductor systems and fabricated wafers. Thus it is critical to develop IIl-nitride films with good electrical properties at growth temperatures compatible with temperature sensitive substrates. High crystal quality GaN films with reduced impurity levels have been achieved at temperatures as low as 500 °C using pulsed growth methods such as atomic layer epitaxy and flow modulation epitaxy (FME). However, the electrical behavior of doped LT Ill-nitride films is relatively unexplored. In this work, thin Si-doped LT GaN films were grown at 550 °C by atmospheric pressure MOCVD using an FME scheme. Triethylgallium and ammonia were used as the GaN precursors and disilane as the Si dopant. Because of the very low growth rate (0.006 A/s), 1200 FME cycles resulted in approximately 16 nm-thick films. Two different FME Si-doping schemes were investigated. The first series varied the fraction of cycles in which disilane was injected into the growing film. Samples were grown with disilane injected every 20, 10, 5, 3, 2, and 1 cycle. The second series varied the disilane flow while using the standard frequency of disilane injection (1 in 5 cycles). Samples were characterized by Hall measurements and secondary ion mass spectrometry (SIMS). For the disilane injection series films, electron concentrations up to 6.97 x 4018 om”? were achieved, with electron mobilities from 34 to 119 cm vi sl The peak electron concentration was achieved for the sample with disilane injected in 1/3 of FME cycles during growth. The charge dropped off for samples with higher frequencies of disilane injection, likely because of degraded morphology. The Si concentrations measured by SIMS were somewhat higher than the electron concentrations measured by Hall. The background atmospheric impurity concentrations averaged 2.1 xX 1017 em’? for oxygen and 3.9 x 10 0 cm ~ for carbon, with no apparent dependence on Si concentration. The disilane flow series resulted in films with electron concentrations from 5.98 x 10 ~ cm ~ to 5.91 x 10'9 om”? and electron mobilities from 52 to 115 cm? vi s |, with the highest charge achieved with the highest disilane flow. The sheet resistance of this sample was 1068 Q/#, which is comparable to low resistance GaN films grown at high temperature, which range from 100-500 Q/#. These results demonstrate the potential for LT Ill-nitrides in electronics applications. This work supported in part by Intel Corporation and the Solid State Lighting and Energy Electronics Center.

High to Ultrahigh Si-Doped GaN Grown by Metalorganic Chemical Vapor Deposition at 550 °C for Heterogeneous Integration

Ferrites and magnetic nanoparticles (NPs) are widely used in sectors such as energy, electronics and biomedicine [1,2]. This work shows an optimum combination of co-precipitation, milling and reduction process of ferrite precursors (CoFe2O4 and NiFe2O4) to obtain CoFe and NiFe NPs, respectively, with tailored magnetic properties and improved heat generation for magneto-thermal applications. Ferrite precursor powders have been synthesized by co-precipitation [3] followed by nanostructuring through self-developed ultrafast milling (24 min). Reduction at different temperatures under Ar+H2 has led to NPs with a tuneable composition going from pure ferrite to CoFe and NiFe NPs, with core-shell nanostructures (CoFe2O4-CoFe and NiFe2O4-NiFe) at intermediate reduction stages. An optimized temperature has resulted in CoFe and NiFe NPs with a high saturation magnetization of 235 and 149 emu/g, respectively. Milling has allowed for diminishing the reduction temperature in 100 °C compared to that required for non-milled particles, which is of relevance in view of upscaling (Fig. 1) [4]. The magneto-thermal response of the NPs has been studied by exposure to alternating magnetic fields at 103 kHz for 5 min. Remarkably, an increase of 28% in the heat generated (under an applied field of 20 mT) has been obtained for the reduced milled CoFe NPs in comparison to the non-milled NPs (Fig. 2), due to particle refinement and high saturation magnetization. The milled NiFe NPs has shown a lower heat generation due to agglomeration effects. This cost-efficient and scalable approach eases the synthesis of NiFe and CoFe NPs for magneto-thermal applications. Acknowledgments. Authors acknowledge financial support from EU M-ERA.NET through COSMAG project (PCI2020-112143); from MICINN through NEXUS project (PID2020-115215RB-C21); and from CM through NanoMagCOST project (P2018/NMT-4321). A.J.C.-H. acknowledges support from "La Caixa" by the Doctoral INPhINIT Incoming program (LCF/BQ/DI20/1178002).

![](https://assets.underline.io/uploads/markdown_image/1/image/3d3878bca20e35efefe648bf0daa5801.jpg)

Fig.1. (a) Room temperature hysteresis loops and (b) XRD patterns of milled cobalt ferrite NPs reduced at different temperatures.

![](https://assets.underline.io/uploads/markdown_image/1/image/1e335e0631e7215287a7642ecf21df92.jpg)

Fig.2. Magneto-thermal measurements of milled and non-milled CoFe NPs.

Scalable Synthesis of CoFe and NiFe Nanoparticles from Ferrite Precursors with Tailored Magneto-Thermal Properties by a Combined Co-precipitation, Milling and Reduction Process

Metal Amorphous Nanocomposites (MANCs) are an evolving class of soft magnetic materials consisting of an Fe- or Co-based crystalline phase embedded in an amorphous matrix. In thin-film form, they possess highly tunable magnetic properties, low eddy current and hysteresis losses, and are capable of performing under high-frequency magnetic field reversal. Therefore they are good candidates for a range of applications including use in power electronics, transformers, and electric motors[1, 2]. We investigated the structural, static and dynamic properties of magnetron sputtered and vacuum annealed (5 minutes and 20 minutes at 520oC) films of CoFeMnNbSiB using Transmission Electron Microscopy (TEM), Atom Probe Tomography (APT), Vibrating Sample Magnetometry (VSM) and Ferro-Magnetic Resonance (FMR). The sputtered films did not show crystallinity, however, an Mn-rich columnar structure that spanned the thickness of the film parallel to the growth direction was observed. After annealing for 5 minutes and 20 minutes, the columnar structure transformed to a partially crystallized microstructure with Co and Fe enriched crystallized phases with ~7nm grain size enclosed by an amorphous intergranular region as shown in Fig. 1. The magnetization dynamics of the films were measured using a custom-built instrument with a frequency range of 1-65 GHz and fields up to 1.6 T. The FMR spectrum of annealed samples shows two overlapping resonances (Fig. 2) due to the two phases present in the samples whereas the as-sputtered sample shows only one resonance. The effective magnetization remained constant whereas the linewidth increased from 13 to 55 Oe after annealing. The magnetic coercivity was observed to be (~26 Oe) independent of annealing while the saturation magnetization increased from 828 to 953 emu/cm3. The observed changes in magnetic properties with annealing indicate that short-time annealing can be useful in optimizing the performance of these MANCs and tailoring properties for various applications.

![](https://assets.underline.io/uploads/markdown_image/1/image/8e0cc2fd197e33d1445aaa05db782123.jpg)

Fig. 1.a) TEM image of 20 minutes annealed sample b) Magnified section of a crystalline region

![](https://assets.underline.io/uploads/markdown_image/1/image/5a0af14f69f8ff951824fdad5f91dd49.jpg)

Fig. 2. FMR spectrum of 20 minutes annealed sample at 40 GHz reflecting two overlapping peaks due to dual-phase in the sample

Structural and magnetic characterization of Co-based soft magnetic amorphous nanocomposite films

Magnetic wires can present outstanding magnetic properties such as giant magnetoimpedance (GMI) or magnetic bistability and related single domain wall (DW) propagation. Magnetically soft glass-coated magnetic microwires prepared by the Taylor-Ulitovsky technique with metallic nucleus covered by flexible, insulating and biocompatible glass are quite demanded for a great number of applications [1]. Recenly, we showed that stress-annealing allows magnetic softening, GMI effect improvement and even grading the magnetic anisotropy in Fe-rich microwires [2]. Although generally thinner wires present certain advantages related to the industrial application, for some applications (like non-contact stress monitoring or magnetic tags) thicker wires are highly requested. Recently, preparation of thicker (above 50 μm in diameter, d) glass-coated Fe-rich microwires is reported [3]. In this paper, we present our recent experimental results on preparation and processing of “thick” Co-rich magnetic microwires (d = 94 μm) with graded magnetic anisotropy. From previous publications related to the effect of stress-annealing on magnetic anisotropy of Fe-rich microwires, is known that the stress-annealing induced anisotropy depends on the annealing temperature, Tann [2]. Such graded magnetic anisotropy has been obtained by stress-annealing of Co-rich microwire at variable annealing temperature. The hysteresis loops for different sections of the microwire have been evaluated using a short (2 mm long) movable pick-up coil. A gradual change in the hysteresis loop (measured by the short pick-up coil) of the sample stress-annealed at variable Tann is observed (see Fig.1). Such microwire, presents also variable squareness ratio, Mr/M0, along the microwire length, L (see Fig.1). Obtained graded anisotropy has been attributed to a gradual modification of the domain structure along the microwire. Previously, for preparation of thin films with a graded magnetic anisotropy, rather sophisticated methods were used, including a change in the chemical composition during the deposition of thin films [4]. Accordingly, we propose a rather simple route to design graded magnetic anisotropy in a magnetic microwire.

![](https://assets.underline.io/uploads/markdown_image/1/image/57c8ead2c65eb757399987363b53f20c.jpg)

Graded magnetic anisotropy in Co-rich microwires

Fe-Nb-Cr-B rapidly quenched melt-spun ribbons (MSRs) show glassy structures in the as-quenched state and Curie temperatures (TC) of 290-330 K depending on the Cr content [1]. The medical applications are usually requiring submicron powders, which can be easily targeted to the sick body organs by means of the external magnetic field [2]. The present work focusses on the preparation of Fe67.2Nb0.3Cr12.5B20 submicron powders by high-energy ball milling from MSRs precursors, using different milling agents: oleic acid (OA), sodium oleate (NAOL) and stearic acid (SA). The main challenge is to preserve the glassy structure from MSRs through the milling process, because only the glassy structure guarantees the low TC. MSRs were annealed at 4000C for 1 h to facilitate the milling. The ratio stainless steel balls:powder was of 50:1. The powders milled in OA and NAOL in the ratio of 1:1 have been washed in n-heptane and dried at 700C in vacuum, while for the ones milled in SA, in the ratio of 5:1, trichloroethylene was used for removing the surfactant. After 150 h of milling in OA the powders have ~100 nm, XRD and UHR-TEM investigations indicating the presence of only the glassy structure and the absence of precipitating crystalline phases. The milling up to 250 h reduces the size of the powders to &lt; 50 nm, while the glassy structure is preserved, as confirmed also by the same TC value (~450C) as for the precursor MSRs. The milling in NAOL keeps the powders in the range of 800÷900 nm, while TC remains ~450C. The milling over 100 h in NAOL results in an increase of TC to 650C and of Ms to 45 Am2/kg, compared with MSRs powders milled in OA (Ms = 35 Am2/kg). The increase of TC and Ms is even more obvious for the powders milled in SA (1100C and 112 Am2/kg, respectively). Moreover, the powders milled in SA are not changing their size even after 50 h of milling, i.e. ~5 µm, comparable with the ones of the precursor MSRs. However, the HR-SEM images indicate round shaped powders after milling in SA, compared with the starting lamellar pieces of MSRs, while the XRD and SAED patterns emphasize similar glassy structures for powders and MSRs. Financial support by the NUCLEU Program (PN 19 28 01 01) is gratefully acknowledged.

Underline digital video library

Gradual Degradation via Dislocation Microloop Formation in InAs Quantum Dot Lasers on Si and GaAs

Effect of the Counter Electrode Material on the SET Kinetics of Ag/HfO2-Based Diffusive Memristors

Effects of Growth Temperature on the Properties of Wafer-Scale Epitaxial MoS2 Monolayers Grown by Metalorganic Chemical Vapor Deposition

Additive Microfabrication of System in Package for Heterogenous Integration with Semiconductor Dies

High In-Content InGaN Platelets as Underlayer for Light-Emitting Diodes Toward Long Wavelength Application

Separation of Defect States and Intrinsic Channel Mobility on the Electrical Operation of IGZO TFTs

Demonstration of Single Crystal InN & GaN/InN Heterostructures by MOCVD

High to Ultrahigh Si-Doped GaN Grown by Metalorganic Chemical Vapor Deposition at 550 °C for Heterogeneous Integration

Scalable Synthesis of CoFe and NiFe Nanoparticles from Ferrite Precursors with Tailored Magneto-Thermal Properties by a Combined Co-precipitation, Milling and Reduction Process

Structural and magnetic characterization of Co-based soft magnetic amorphous nanocomposite films

Graded magnetic anisotropy in Co-rich microwires

Influence of wet and dry milling conditions on the evolution of microstructure and TC of Fe-Cr-Nb-B glassy powders

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES