Electrical Properties of Ultrathin Platinum Films by Plasma-Enhanced Atomic Layer Deposition

Advanced Atomic Layer Modulation Based Highly Homogeneous PtRu Precious Metals Alloy Thin Films

Atomic layer modulation (ALM) presents a novel approach for controlling the stoichiometry of platinum-ruthenium (PtRu) alloys rather than a tedious atomic layer deposition (ALD) supercycling multielement ALD process. This method sequentially pulses dimethyl-(N,N-dimethyl-3-butene-1-amine-N)platinum (C8H19NPt, DDAP) and tricarbonyl(trimethylenemethane)ruthenium [Ru(TMM)(CO)3] precursors with O2 as a counter reactant at 225 °C to produce ALM-PtRu bimetallic alloys at the nanoscale. By smartly adjusting precursor pulsing times and temperatures, the average surface composition during growth can be modulated, achieving precise control over the PtRu alloy stoichiometry. Aberration-corrected ultra-high-resolution scanning transmission electron microscope, Rutherford backscattered spectrometry, and advanced X-ray diffraction analytical tools demonstrate homogenized Pt and Ru elemental distribution without localized segregation with adjustable Pt:Ru ratios ranging from 28:72 to 97:3. Demonstrating ≈100% step coverage on the high aspect ratio (≈30) 3D trench structures (top width of 125 nm, bottom width of 85 nm), the alloy maintains uniform thickness (≈30 nm) throughout its layers. ALM-PtRu demonstrates durable and superior electrocatalytic performance compared to benchmark precious metal catalysts like ALD-Pt and ALD-Ru. This study highlights ALM's potential for precise alloy stoichiometry in PtRu films, offering significant promise for various applications, particularly electrocatalysis, and extending ALM to other metallic alloy systems.

Orotic acid-capped Tb(III)-doped calcium sulphate nanorods for the selective detection of tryptophan

Lanthanide-based luminescent materials have gained huge attention due to their applications in optoelectronic devices, sensing, bio-imaging, anti-counterfeiting, and more. In this work, we report a luminescence-based sensor for the detection of tryptophan using orotic acid-capped Tb3+-doped CaSO4 nanorods (NRs). Orotic acid (OA) was found to play a dual role as a capping agent to control the growth of the nanorods and as a sensitizer for Tb3+ ions. The resulting nanorods exhibited excellent dispersibility and strong photoluminescence signals characteristic of Tb3+ ions in the visible region. Nearly 10-fold enhancement in the emission intensity was noted through OA sensitization compared to direct excitation of Tb3+ ions (acceptors). Interestingly, the strong emission intensity of the NRs reduced significantly with the addition of tryptophan. In contrast, hardly any change was noted with the addition of other amino acids and metal ions, suggesting greater selectivity for tryptophan. Moreover, there is barely any notable interference from other amino acids toward the detection of tryptophan. The limit of detection is found to be ∼0.61 μM. Finally, the sensing study was extended to biological samples to detect tryptophan present in blood plasma, urine, and saliva samples. The nanorods demonstrated high detection abilities, indicating the potential of the developed materials for biomedical applications.

Development of a Microheater with a Large Heating Area and Low Thermal Stress in the Heating Area

In this paper, a microheater that can absorb thermal stress and has a large heating area is demonstrated by optimizing the structure and process of the microheater. Four symmetrically distributed elongated support beam structures were machined around the microheater via deep silicon etching. This design efficiently mitigates the deformation of the heated region caused by thermal expansion and enhances the structural stability of the microheater. The updated microheater no longer converts the work area into a thin film; instead, it creates a stable heating platform that can uniformly heat a work area measuring 10 × 10 mm2. The microheater is verified to have high temperature uniformity and structural stability in finite element simulation. Finally, thorough investigations of electrical-thermal-structural characterization were conducted. The test findings show that the new microheater can achieve 350 °C with a power consumption of 6 W and a thermal reaction time of 22 s. A scan of its whole plane reveals that the surface of the working area of the new microheater is flat and does not distort in response to variations in temperature, offering good structural stability.

Efficient ultrafast field-driven spin current generation for spintronic terahertz frequency conversion

Efficient generation and control of spin currents launched by terahertz (THz) radiation with subsequent ultrafast spin-to-charge conversion is the current challenge for the next generation of high-speed communication and data processing units. Here, we demonstrate that THz light can efficiently drive coherent angular momentum transfer in nanometer-thick ferromagnet/heavy-metal heterostructures. This process is non-resonant and does neither require external magnetic fields nor cryogenics. The efficiency of this process is more than one order of magnitude higher as compared to the recently observed THz-induced spin pumping in MnF2 antiferromagnet. The coherently driven spin currents originate from the ultrafast spin Seebeck effect, caused by a THz-induced temperature imbalance in electronic and magnonic temperatures and fast relaxation of the electron-phonon system. Owing to the fact that the electron-phonon relaxation time is comparable with the period of a THz wave, the induced spin current results in THz second harmonic generation and THz optical rectification, providing a spintronic basis for THz frequency mixing and rectifying components.

Thermal Interface Enhancement via Inclusion of an Adhesive Layer Using Plasma-Enhanced Atomic Layer Deposition

Interfaces govern thermal transport in a variety of nanostructured systems such as FinFETs, interconnects, and vias. Thermal boundary resistances, however, critically depend on the choice of materials, nanomanufacturing processes and conditions, and the planarity of interfaces. In this work, we study the interfacial thermal transport between a nonreactive metal (Pt) and a dielectric by engineering two differing bonding characters: (i) the mechanical adhesion/van der Waals bonding offered by the physical vapor deposition (PVD) and (ii) the chemical bonding generated by plasma-enhanced atomic layer deposition (PEALD). We introduce 40-cycle (∼2 nm thick), nearly continuous PEALD Pt films between 98 nm PVD Pt and dielectric materials (8.0 nm TiO₂/Si and 11.0 nm Al₂O₃/Si) treated with either O₂ or O₂ + H₂ plasma to modulate their bonding strengths. By correlating the treatments through thermal transport measurements using time-domain thermoreflectance (TDTR), we find that the thermal boundary resistances are consistently reduced with the same increased treatment complexity that has been demonstrated in the literature to enhance mechanical adhesion. For samples on TiO₂ (Al₂O₃), reductions in thermal resistance are at least 4% (10%) compared to those with no PEALD Pt at all, but could be as large as 34% (42%) given measurement uncertainties that could be improved with thinner nucleation layers. We suspect the O₂ plasma generates stronger covalent bonds to the substrate, while the H₂ plasma strips the PEALD Pt of contaminants such as carbon that gives rise to a less thermally resistive heat conduction pathway.