Magnetism in Nanocrystalline Gold

While bulk gold is well known to be diamagnetic, there is a growing body of convincing experimental and theoretical work indicating that nanostructured gold can be imparted with unconventional magnetic properties. Bridging the current gap in experimental study of magnetism in bare gold nanomaterials, we report here on magnetism in gold nanocrystalline films produced by cluster deposition in the aggregate form that can be considered as a crossover state between a nanocluster and a continuous film. We demonstrate ferromagnetic-like hysteretic magnetization with temperature dependence indicative of spin-glass-like behavior and find this to be consistent with theoretical predictions, available in the literature, based on first-principles calculations

Low-Temperature Atomic Layer Deposition of Low-Resistivity Copper Thin Films Using Cu(dmap)₂ and Tertiary Butyl Hydrazine

Herein, we describe a process for the low-temperature atomic layer deposition of copper using Cu­(dmap)₂ (dmap = dimethylamino-2-propoxide). The use of tertiary butyl hydrazine (TBH) as the reducing agent was found to have a significant improvement on the purity and the resistivity of the Cu films compared to previous processes. Our process was studied at low temperatures of 80–140 °C on native oxide terminated Si. At 120 °C, self-limiting Cu deposition was demonstrated with respect to both Cu­(dmap)₂ and TBH pulse lengths. During the initial stages of the deposition (125–1000 cycles), a growth rate of 0.17 Å/cycle was measured. Once the substrate surface was completely covered, deposition proceeded with a more moderate growth rate of 0.05 Å/cycle. According to X-ray diffraction, the films were crystalline cubic Cu with a slight preference toward (111) orientation. Based on scanning electron micrographs, the Cu films were relatively smooth with the roughness increasing as a function of both increasing temperature and thickness. A 54 nm film deposited at the low temperature of 120 °C exhibited a low resistivity of 1.9 μΩ·cm. Composition analysis on this film showed a remarkably high purity of approximately 99.4 at.%, with the rest being hydrogen and oxygen. The films could be deposited also on hydrogen terminated Si, glass, Al₂O₃, TiN, and Ru, extending the suitability of the process to a wide range of applications

Preparation of Lithium Containing Oxides by the Solid State Reaction of Atomic Layer Deposited Thin Films

Lithium containing multicomponent oxides are important materials for both lithium-ion batteries and optical applications. In most cases thin films of these materials are desired. Atomic layer deposition (ALD) is a thin film deposition method that is known to deposit high quality films by sequential self-limiting surface reactions. However, the reactivity of lithium ions during the deposition process can pose challenges for the control of the film growth and even destroy the self-limiting nature of ALD completely. In this paper, we have studied the combination of atomic layer deposition and solid state reactions for the generation of lithium containing multicomponent oxide films. Atomic layer deposited transition metal oxide thin films were covered with ALD-grown lithium carbonate, and the films were annealed to produce lithium tantalate, titanate, and niobate. Lithium carbonate was chosen as the source of lithium because it is easy to deposit by ALD and can be handled in air. The films were analyzed as-deposited and after annealing using grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), and time-of-flight elastic recoil detection analysis (ToF-ERDA). By this method we were able to produce crystalline and very close to stoichiometric films of LiTaO₃, Li₂TiO₃, and LiNbO₃. The films showed only small amounts of carbon and hydrogen impurities after annealing. After prolonged annealing at high temperatures, lithium silicates began to form as a result of lithium ions reacting with the silicon substrates

Heteroleptic Cyclopentadienyl-Amidinate Precursors for Atomic Layer Deposition (ALD) of Y, Pr, Gd, and Dy Oxide Thin Films

Thin films of rare-earth (RE) oxides (Y₂O₃, PrO_<i>x</i>, Gd₂O₃, and Dy₂O₃) were deposited by atomic layer deposition from liquid heteroleptic RE­(<i>ⁱ</i>PrCp)₂(<i>ⁱ</i>Pr-amd) precursors with either water or ozone as the oxygen source. Film thickness, crystallinity, morphology, and composition were studied. Saturation was achieved with Gd₂O₃ when O₃ was used as the oxygen source at 225 °C and with Y₂O₃ with both oxygen sources at as high temperature as 350 °C. The growth rates were 0.90–1.3 Å/cycle for these processes. PrO_<i>x</i> was challenging to deposit with both oxygen sources but with long, 20 s purges after the water pulses uniform films could be deposited. However, saturation was not achieved. With Dy₂O₃, uniform films could be deposited and the Dy­(<i>ⁱ</i>PrCp)₂(<i>ⁱ</i>Pr-amd)/O₃ process was close to saturation at 300 °C. The different oxygen sources had an effect on the crystallinity and impurity contents of the films in all the studied processes. Whether ozone or water was better choice for oxygen source depended on the metal oxide material that was deposited

Electric and Magnetic Properties of ALD-Grown BiFeO₃ Films

The magnetization and electric polarization in thin bismuth ferrite films (BFO) films have been under extensive study for high technological potential of single-phase multiferroic materials. Surpassing the antiferromagnetic nature and weak magneto-electric coupling of bulk BFO has required highly specialized substrates and epitaxial growth methods so far. Polycrystalline single-phase multiferroic BFO (50–500 nm thick) films were grown by atomic layer deposition (ALD) on technologically simple Pt/SiO₂/Si substrates. The BFO films were found to exhibit strong saturating ferromagnetism and coercivity at temperatures ranging from cryogenic to room temperature even with 500 nm thick layers, a property which cannot be obtained with thick epitaxial films or bulk BFO. The magnetization mechanism was associated with magnetic domain wall dynamics and collapsing of the helimagnetic spin modulation. The electric properties were found to be strongly dependent on the film thickness. The film crystallization, composition, and chemical state have been analyzed by various techniques. The magnetic and ferroelectric properties were determined by using a SQUID magnetometer and a ferroelectricity tester. The results of the work indicate clearly that the ALD technique offers an efficient way for synthesis of polycrystalline BFO films and for tailoring their electromagnetic properties