We report a synthesis of colloidal nanostructures combining a magnetic material (FePt) with a narrow-gap semiconductor (PbS and PbSe) in form of core−shells or nanodumbbells and explore their optical, magnetic, electrical, and magnetotransport properties. The arrays of “magnet-in-the-semiconductor” nanostructures show semiconductor-type transport properties with magnetoresistance typical for magnetic tunnel junctions, thus combining the advantages of both functional components. We observed gate-controlled charge transport through the arrays of FePt−PbS and FePt−PbSe core−shell nanostructures with an electron mobility of 0.01 cm2/(V s) and 0.08 cm2/(V s), respectively, combined with ferro- and superparamagnetic behavior and large tunneling magnetoresistance. This work shows that multicomponent colloidal nanostructures can be used as the building blocks for design of multifunctional materials for electronics and optoelectronics.

"Magnet-in-the-semiconductor" FePt-PbS and FePt-PbSe nanostructures: magnetic properties, charge transport, and magnetoresistance.

In this work, the influence of substrate bias voltage on the microhardness, adhesive strength, friction coefficient, and wear rate of AIP Cr2O3 films deposited on AISI 304 stainless steel substrates was investigated systematically. In the meantime, the wear failure mechanism of AIP Cr2O3 films in dry sliding contact was also analyzed and discussed. The results showed that the mechanical properties, adhesive behaviors, and tribological performance of AIP Cr2O3 films were greatly altered by applying a negative bias voltage. With increasing the bias voltage, the hardness, critical load, and tribological performance of AIP Cr2O3 films first were improved gradually, and then were impaired slightly again. When the bias voltage is - 100 V. the Cr2O3 film possessed the highest hardness, the strongest adhesion, and the best wear resistance. The essence of above phenomena was attributed to the variations of microstructure and defect density in the films induced by the substrate bias voltage increase. The main wear failure mechanism of AIP Cr2O3 films is crack initiation and propagation under the high contact stresses, inducing the local film with small area to flake off gradually, and eventually leading to the formation of a wear scar. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Study on nanocrystalline Cr2O3 films deposited by arc ion plating: II. Mechanical and tribological properties

Intracellular catalytic reactions can tailor tumor cell plasticity toward high-efficiency treatments, but the application is hindered by the low efficiency of intracellular catalysis. Here, a magneto-electronic approach is developed for efficient intracellular catalysis by inducing eddy currents of FePt-FeC heterostructures in mild alternating magnetic fields (frequency of f = 96 kHz and amplitude of B ≤ 70 mT). Finite element simulation shows a high density of induced charges gathering at the interface of FePt-FeC heterostructure in the alternating magnetic field. As a result, the concentration of an essential coenzyme-β-nicotinamide adenine dinucleotide-in cancer cells is significantly reduced by the enhanced catalytic hydrogenation reaction of FePt-FeC heterostructures under alternating magnetic stimulation, leading to over 80% of senescent cancer cells-a vulnerable phenotype that facilitates further treatment. It is further demonstrated that senescent cancer cells can be efficiently killed by the chemodynamic therapy based on the enhanced Fenton-like reaction. By promoting intracellular catalytic reactions in tumors, this approach may enable precise catalytic tumor treatment.

Magneto-Electrically Enhanced Intracellular Catalysis of FePt-FeC Heterostructures for Chemodynamic Therapy

Surface tension-driven self-alignment is a passive and highly-accurate positioning mechanism that can significantly simplify and enhance the construction of advanced microsystems. After years of research, demonstrations and developments, the surface engineering and manufacturing technology enabling capillary self-alignment has achieved a degree of maturity conducive to a successful transfer to industrial practice. In view of this transition, a broad and accessible review of the physics, material science and applications of capillary self-alignment is presented. Statics and dynamics of the self-aligning action of deformed liquid bridges are explained through simple models and experiments, and all fundamental aspects of surface patterning and conditioning, of choice, deposition and confinement of liquids, and of component feeding and interconnection to substrates are illustrated through relevant applications in micro- and nanotechnology. A final outline addresses remaining challenges and additional extensions envisioned to further spread the use and fully exploit the potential of the technique.

https://pubs.rsc.org/en/content/articlepdf/2017/sm/c6sm02078j

Surface tension-driven self-alignment

Evolution of physical properties in hafnium carbonitride thin films

New surface mounting and packaging technologies, using self-assembly with chips having cavity structures, were investigated for three-dimensional (3D) and hetero integration of complementary metal-oxide semiconductors (CMOS) and microelectromechanical systems (MEMS). By the surface tension of small droplets of 0.5 wt% hydrogen fluoride (HF) aqueous solution, the cavity chips, with a side length of 3 mm, were precisely aligned to hydrophilic bonding regions on the surface of plateaus formed on Si substrates. The plateaus have micro-channels to readily evaporate and fully remove the liquid from the cavities. The average alignment accuracy of the chips with a 1 mm square cavity was found to be 0.4 mm. The alignment accuracy depends, not only on the area of the bonding regions on the substrates and the length of chip periphery without the widths of channels in the plateaus, but also the area wetted by the liquid on the bonding regions. The precisely aligned chips were then directly bonded to the substrates at room temperature without thermal compression, resulting in a high shear bonding strength of more than 10 MPa.

https://www.mdpi.com/2072-666X/2/1/49/pdf

Self-Assembly of Chip-Size Components with Cavity Structures: High-Precision Alignment and Direct Bonding without Thermal Compression for Hetero Integration

A new magnetic nanodot (MND) memory with FePt nanodots was proposed. The FePt nanodots dispersed in SiO2 insulating film was successfully fabricated by self-assembled nanodot deposition (SAND). The size of the FePt nanodot can be controlled by SAND with a different target area ratio of the FePt pellets area in the SiO2 target. Thermal annealing converts the magnetic properties of the FePt nanodots from antiferromagnetic into high coercivity ferromagnetic without thermal agglomeration. An L10 face-centered tetragonal (fct) FePt MND film was successfully formed which acted as a charge retention layer. Furthermore, the fundamental characteristics of the MND memory were investigated using magnetic metal oxide semiconductor (MOS) capacitor devices.

https://iopscience.iop.org/article/10.1143/JJAP.46.2167/pdf

New magnetic nanodot memory with FePt nanodots

A novel flash memory which has FePt magnetic floating gate was proposed. An FePt magnetic floating gate with a high coercivity was successfully fabricated by DC magnetron sputtering with rapid thermal annealing. As for magnetic properties, the switching magnetic fields of 21 Oe for the NiFe film and 1600 Oe for the FePt film were employed for the control gate and the floating gate materials, respectively. The fundamental characteristics of the magnetic flash memory were confirmed using magnetic metal oxide semiconductor (MOS) capacitor devices and magnetic tunneling diode (MTD) devices.

New magnetic flash memory with FePt magnetic floating gate

Plasma- and water-assisted oxide-oxide thermocompression direct bonding for a self-assembly based multichip-to-wafer (MCtW) 3D integration approach was demonstrated. The bonding yields and bonding strengths of the self-assembled chips obtained by the MCtW direct bonding technology were evaluated. In this study, chemical mechanical polish (CMP)-treated oxide formed by plasma-enhanced chemical vapor deposition (PE-CVD) as a MCtW bonding interface was mainly employed, and in addition, wafer-to-wafer thermocompression direct bonding was also used for comparison. N2 or Ar plasmas were utilized for the surface activation. After plasma activation and the subsequent supplying of water as a self-assembly mediate, the chips with the PE-CVD oxide layer were driven by the liquid surface tension and precisely aligned on the host wafers, and subsequently, they were tightly bonded to the wafers through the MCtW oxide-oxide direct bonding technology. Finally, a mechanism of oxide-oxide direct bonding to support the previous models was discussed using an atmospheric pressure ionization mass spectrometer (APIMS).

Oxide-Oxide Thermocompression Direct Bonding Technologies with Capillary Self-Assembly for Multichip-to-Wafer Heterogeneous 3D System Integration.

A multiple alloy metal nano-dots memory using FN tunneling was investigated in order to confirm its structural possibility for future flash memory. In this work, a multiple FePt nano-dots device with a high work function (~5.2 eV) and extremely high dot density (~1.2 × 1013 cm−2) was fabricated. Its structural effect for multiple layers was evaluated and compared to the one with a single layer in terms of the cell characteristics and reliability. We confirm that MOS capacitor structures with two to four multiple FePt nano-dot layers provide a larger threshold voltage window and better retention characteristics. Furthermore, it was also revealed that several process parameters for block oxide and inter-tunnel oxide between the nano-dot layers are very important to improve the efficiency of electron injection into multiple nano-dots. From these results, it is expected that a multiple FePt nano-dots memory using Fowler–Nordheim (FN) tunneling could be a candidate structure for future flash memory.

https://iopscience.iop.org/article/10.1088/0268-1242/24/8/085013/pdf

Ji Chel Bea

Papers

Self-Assembly of Chip-Size Components with Cavity Structures: High-Precision Alignment and Direct Bonding without Thermal Compression for Hetero Integration

New magnetic nanodot memory with FePt nanodots

New magnetic flash memory with FePt magnetic floating gate

Oxide-Oxide Thermocompression Direct Bonding Technologies with Capillary Self-Assembly for Multichip-to-Wafer Heterogeneous 3D System Integration.

Cell characteristics of a multiple alloy nano-dots memory structure