In this work, a comprehensive framework for predicting etching behavior is developed using the test case of hafnium lanthanate (Hf_xLa_yO_z) in Cl₂/BCl₃ chemistry, starting from detailed thermodynamic analysis in the form of volatility diagrams. Through these calculations, it was predicted that at typical plasma reactor operating pressures, the reactions of molecular Cl₂ and Cl radicals with La₂O₃ and HfO₂ could generate sufficiently high partial pressures of O_xCl_y for measurable material removal to occur.

The etch rate of Hf_0.25La_0.12O_0.63 as a function of ion energy was characterized in situ using a quartz crystal microbalance. The etch rate data was found to exhibit a dual ion energy dependence with a maximum etch rate of ~27 Å/min at E_ion = 175 eV. The overall etch rate was found to be approximately half that of a pure HfO₂ film etched at the same conditions, due to the formation of non-volatile LaCl_x compounds.

QMS measurements of HfLaO in Cl₂ chemistry showed LaOCl and LaCl as the primary La-containing etch products. XPS analysis of pure La₂O₃ films provided further evidence of this hypothesis, showing significant Cl retention (~10%) compared to HfLaO and also revealing the presence of Cl-O-La bonding. A kinetics-based bulk scale (TML) model was fit to the aforementioned experimental data and good agreement was shown between the TML model's simulated results and etch rate data. An additional degree of validation was provided through a comparison of the model's predicted composition of the surface mixing layer and the XPS-measured film compositions after plasma exposure.

The final validation of this approach was to assess the fitted kinetic parameters for complex oxide etching in Cl-based chemistry (such as reaction rate coefficients, threshold energies and sticking probabilities) at feature scale levels. The results from the TML model were coupled to a Monte Carlo based feature profile simulator and used to predict the variation of the etched feature profiles of Hf_0.25La_0.12O_0.63 films for varying aspect ratios (1.5, 3 and 6) and ion energies (75, 100 and 175 eV). In order to compare to experimental results, features of varying aspect ratio were achieved using an e-beam tool to pattern a ZEP520A photoresist mask on HfLaO followed by etching in Cl₂ . Good agreement was achieved with the etched profile at 100 eV and AR = 5. As a test of the model's ability to handle variations in gas chemistry with a material system besides that of high-k dielectrics, this methodology was also applied to the shallow trench isolation process (Si etching in Cl₂2/O₂ chemistry). The model showed good fitting of the major process parameters (etch rate, etch product ratios and surface composition) and showed an ability to predict the profile variation with 0, 2, 6 and 8% oxygen addition to a pure Cl₂ plasma for the etching of Si.

Core/shell nanorods based on a plasmonic gold nanorod core with a thin dielectric shell were designed, synthesized and characterized to demonstrate their potential in photovoltaics and cancer therapy applications.

For solar cell applications, the light scattering properties of Au nanorods were combined with an electrically insulating silica (SiO₂ ) layer to form a core/shell architecture. The Au nanorod core was coated with a SiO₂ shell in order to isolate the conductive metal surface of the gold from the conductive photo-polymers in the active layers of organic photovoltaic (OPV) devices. The aspect ratio of the Au nanorod core was spectrally tailored so that the peak extinction wavelength of the Au/SiO₂ core/shell nanorod coincided with wavelength regions in which the photovoltaic material absorbed poorly. Specifically, octadecyltrimethoxysilane (OTMS)-functionalized Au/SiO₂ core/shell nanorods were spectrally tailored and incorporated into two OPV polymer systems: poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCB60M) and poly[2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,4-b]dithiophene-alt-5-dibutyloctyl-3,6-bis(5-bromothiophen-2-yl) pyrrolo[3,4-c]pyrrole-1,4-dione] (PBDTT-DPP:PC60BM). For the P3HT:PC60BM polymer with a band edge at ~ 670 nm, the incorporation of Au/SiO2 core/shell nanospheres (radius = 20 nm) resulted in a 2.7% improvement in photon conversion efficiency (PCE). The incorporation of the core/shell nanorods (radius = 10 nm) with an aspect ratio (AR) ~ 2.5 (extinction peak, ëpeak = 670 nm) resulted in a 7.1% improvement in PCE. For the PBDTT-DPP:PC60BM polymer with a band edge at ~ 830 nm, the incorporation of Au/SiO₂ core/shell nanospheres resulted in a 9.2% improvement, while that of core/shell nanorods (radius = 8 nm) of AR ~ 4 (extinction peak, ëpeak = 830 nm) resulted in a 14.4% improvement in PCE. The performance enhancements were corroborated by external quantum efficiency (EQE) measurements.

For cancer therapy applications, the strong light absorption properties of Au nanorods were combined with the upconverting light emission properties of rare earth doped-yttria (RE:Y₂O₃) in order to create hybrid plasmonic/fluorescent core/shell nanorods for dual bio-imaging and photo-thermal therapy applications. Specifically, Au/SiO₂/Yb:Er:Y₂O₃ core/shell nanorods were synthesized, optically characterized and tested for photo-thermal therapy both in-vitro and in-vivo. The plasmonic/fluorescent Au/SiO₂/Yb:Er:Y₂O₃ core/shell nanorods have a unique optical signature when excited with 980 nm laser irradiation, exhibiting both the broadband photoluminescence characteristic of Au interband transitions and the sharp emission lines characteristic of the Er^{3+ 4}F_9/2 -> ⁴I_15/2 energy transition. The Au/SiO₂/Yb:Er:Y₂O₃ showed a nearly two fold increase in emission compared to SiO₂/Yb:Er:Y₂O₃ nanospheres at a wavelength of 655 nm (Er^{3+ 4}F_9/2 -> ⁴I_15/2 energy transition). Au/SiO₂/Yb:Er:Y₂O₃ core/shell nanorods were shown to exhibit photothermal properties upon 980 nm laser irradiation which reduced cell viability in cyto-toxicity assays and induced selective hyperthermia in breast cancer cells both in-vitro and in-vivo.

This work focuses on the design, synthesis, characterization and integration of multiferroic composite materials via radical-enhanced atomic layer deposition (RE-ALD). Specifically, ferrimagnetic CoFe2O4 is integrated with multiferroic BiFeO3 and ferroelectric HfO2 (FE-HfO2), respectively, to create two distinct composite systems. The use of multiferroic BiFeO3 as the ferroelectric phase offers the potential of employing two interfacial coupling phenomena simultaneously. On the other hand, desirable ferroelectric property and superior Si-compatibility that FE-HfO2 can offer make it an intriguing material system for further implementation into device processing at an industrial scale.

In the CoFe2O4/BiFeO3 system, high-quality CoFe2O4 and BiFeO3 were synthesized on SrTiO3 (001) substrates via RE-ALD using TMHD-based metalorganic precursors (TMHD = 2,2,6,6-tetramethylheptane-3,5 dione) and atomic oxygen. With post-deposition thermal treatments, BiFeO3 exhibited epitaxial single-crystalline growth in its (001)pc orientation. Ferroelectric switching and measurable ferromagnetism confirmed the multiferroicity of BiFeO3. CoFe2O4 exhibited textured-polycrystalline growth with a ~10-nm epitaxial transition layer, which led to tunable ferrimagnetism with a thickness-related strain relaxation process. The CoFe2O4 thin films exhibited magnetic behavior that is comparable with the ones synthesized by other processing techniques as well as bulk crystals. Nano-laminates of CoFe2O4/BiFeO3 in 2D-2D configuration were synthesized on SrTiO3 (001) and Si (001) substrates. By fixing the nanolaminate total thickness at 55 nm and CoFe2O4-BiFeO3 ratio at a constant of CoFe2O4:BiFeO3 = 15:40 while increasing the number of alternating layers up to 5 layers, the tri-layer BiFeO3/CoFe2O4/BiFeO3 structure exhibits the most promising functional properties with an optimized polarization ~17 μC/cm2 and saturation magnetism (Ms) ~125 emu/cm3. Both strain and magnetic interactions were observed at the interface for the nano-laminates due to the multiferroic nature of BiFeO3. The tri-layer structure exhibited a converse magnetoelectric coupling coefficient (αconverse) of ~22 Oe cm/kV. By scaling the nano-laminate from ~55 nm to ~16 nm in total thickness, αconverse is further improved to ~64 Oe cm/kV, comparable with systems reported with much higher thicknesses. As the first demonstration of a fully ALD-synthesized multiferroic composite, this part of the work reveals the possibility to utilize ALD to optimize multiferroic nano-laminates for further integrations into magnetoelectric devices.

For CoFe2O4/FE-HfO2 composites, HfO2 thin films were synthesized with tetrakis(dimethylamido)hafnium(IV) (TDMAH) and atomic oxygen. In this design, CoFe2O4 served not only as the mechanical confinement layer but also as an active magnetic layer that contributed to overall magnetism. For ~6nm HfO2 annealed at ~700 �C, the CoFe2O4/FE-HfO2 composites exhibited a remnant polarization (Pr) ~5.5 μC/cm2 and an electrical coercivity (Ec) ~2000 kV/cm as well as an out-of-plane magnetic anisotropy with a saturation magnetization (Ms) of ~155 emu/cm3 and a magnetic coercivity (Hc) ranging from ~1000-3400 Oe. Magnetoelectric characterization revealed promising magnetoelectric coupling, with αconverse ranged 55-168 Oe cm/kV at room-temperature, once again is comparable with other systems reported with much higher thicknesses. It is believed that the CoFe2O4/FE-HfO2 system here opens many new avenues for developing future magnetoelectric composites and related devices.

This work focuses on the development of atomic layer deposition (ALD) for lead zirconate titanate, Pb(ZrxTi1-x)O3 (PZT). Leveraging the surface-reaction controlled process based on alternating self-limiting surface reactions, PZT can be synthesized not only with elemental precision to realize the desired composition (Zr/Ti = 52/48) but also with outstanding conformality. The latter enables the integration of PZT with a ferromagnetic phase to realize multiferroism (MF) and magnetoelectric (ME) effect. Since PZT is one of the best known ferroelectric and piezoelectric materials due the large displacements of the Pb ions at the morphotropic phase boundary, PZT based MF composites could lead to stronger ME coupling through strain coupling at the interface.

Specifically, ALD PZT thin films were synthesized by using beta-diketonate metalorganic precursors Pb(TMHD)2, Zr(TMHD)4, and Ti(O.i-Pr)2(TMHD)2 and H2O. The number of local cycles and global cycles were regulated to achieve the desired stoichiometry and thickness, respectively. ALD of PZT was studied to obtain (100) textured PZT on Pt (111) oriented platinized silicon substrates. In order to attain a highly oriented PZT thin film, a (100) textured PbTiO3 seed layer was required because PZT orientation is governed by nucleation.

MF nanocomposites were engineered using ALD PZT thin films to achieve controlled complex nanoscale structures, enabling porosity to be studied as a new additional parameter for nancomposite architectures to enhance ME effect. Specifically, 3-6 nm-thick ALD PZT thin films were deposited to uniformly coat the walls of mesoporous cobalt ferrite (CFO) template. The PZT/CFO nanocomposites were electrically poled ex-situ and the change in magnetic moment was measured. The inverse magnetoelectric coupling coefficient, α, was determined to be 85.6 Oe-cm/mV. The in-plane results show no significant change in magnetization (1–4%) as a function of electric field, which was expected due to the effect of substrate clamping. The out-of-plane magnetization showed that the mesoporous CFO coated with 3-nm-thick PZT film had a greater saturation magnetization change of 15% compared to 10% for the 6-nm-thick PZT film. This indicates that the flexibility in the partially filled pores enhances the ME coupling.

Additionally, ALD PZT films were integrated between MgO and CoFeB layers to fabricate magnetic tunnel junctions (MTJ), which was the first work to demonstrate increased voltage controlled magnetic anisotropy (VCMA) effect in a complete MTJ stack using a high dielectric material within the tunnel barrier and exhibit sizeable tunneling magnetoresistance (TMR) at room temperature. The fabricated PZT MTJs with the MgO/PZT/MgO barrier demonstrated a VCMA coefficient which is ~40% higher (20 fJ/V-m) than MgO MTJs (14 fJ/V-m) and TMR of more than 50% at room temperature, comparable to that of the MgO MTJs. The enhanced VCMA coefficient and sizeable TMR makes PZT MTJs potential candidates for future voltage-controlled, ultralow-power magnetic random access memory devices.

ALD enables the growth of conformal ultra-thin PZT films, which can then be integrated to engineer nanoscale multiferroic composites for various applications.

This work demonstrated a generalizable approach for patterning metals on the nanometer scale. As the complexity of device structures keeps evolving, corresponding etching techniques need to be developed to accommodate the integration of new materials on ever-shrinking scales. The contrast in chemical reactivity is explored and leveraged as the source of etching selectivity in the illustrated atomic layer etching (ALE) process to meet the increasingly stringent dimension requirements on etch-resistant metals.

Thermodynamic assessments are performed on Ni to screen and predict the potential solution and gas-phase etchants. Organic etchants such as acetic acid, formic acid, acetylacetone, and hexafluoro-acetylacetone were screened to etch Ni and NiO in the solution phase. In concentrated solutions of formic acid, NiO was observed to etch selectively over metallic Ni at values up to 30. Such selectivity is further explored in the gas-phase via a sequential oxidation-etch process. Cyclic oxygen plasma and gas phase formic acid exposures resulted in an etch rateof 2.3 nm/cycle. A high (>100) gas-phase etch selectivity of NiO over Ni by this cyclic process is achieved, fulfilling the self-limiting requirement of an Atomic Layer Etching (ALE) process. Anisotropic etch profile for Ni thin film with SiO2 hard mask was achieved through this cyclic process and the final feature sidewall was measured to be close to 90�. This ALE approach is further facilitated by a prior RIE chemistry to realize highly directional removal at a high throughput. Density Functional Theory (DFT) simulation was conducted, and Ni thin film with an oxygen underlayer was calculated to be the configuration that enables favorable etching reaction with the presence of formic acid vapor.

A similar cyclic approach was applied to the patterning of Cu thin film and directional removal was also achieved. An average etch rate of 2.4 nm/cycle was determined experimentally. LMM Auger signal was used to confirm the change in Cu surface states from Cu dominant (as deposited) to CuO dominant (after oxidation) to Cu(OH)2 dominant (after etching). DFT based simulation was established with the most energetically stable Cu, CuO and Cu(OH)2 configurations. The most favorable etch product was determined to be Cu2(HCOO)4 dimer with a formic acid exposure partial pressure window of 150 Torr ~ 250 Torr. Experimental verification of the gas phase etching products was attempted, and Cu was detected in the etch product.

Manipulating atoms to form desired structures on an atomic scale has long been the ultimate goal of the semiconductor industry, as it would open up infinite possibilities for device innovation and manufacturing. The new ALE chemistry introduced in this work adds an essential piece of the puzzle to the bigger picture and brings the goal one step closer. It is believed that with the implementation and further optimization of the demonstrated ALE process, atomistic subtraction of metals would be eventually realized.

Key to the continued scaling of electronic devices is the efficient control of magnetism with electric fields. In this work, multiple routes of achieving this control are explored, including CoFeB/MgO-based magnetic tunnel junctions to be incorporated into next-generation magnetoelectric random-access memory arrays and FeGa/NiFe-based magnetic multilayers to be incorporated into microscale magnetoelectric antennae.

For the magnetic tunnel junction application, this work verifies that the VCMA effect is greatly affected by the quality of the CoFeB/MgO interface and suggests that both the interfacial oxidation and crystallinity of the CoFeB layer are key factors in optimizing the VCMA characteristics of CoFeB/MgO-based MeRAM material systems. Furthermore, the successful integration of CoFeB with single-crystal MgO substrates is a substantial step toward achieving a greater degree of crystallinity in magnetic memory technologies.

For microscale magnetoelectric antennae, magnetic multilayer composites were synthesized in an attempt to combine the complementary properties of FeGa and NiFe and create an optimal magnetoelastic material. These multilayers combine the low magnetic loss at high frequency of NiFe with the strong magnetoelastic coupling of FeGa, and the properties were optimized by varying the thin film deposition conditions, thickness, and composition, and the resulting properties are well-suited for high-frequency applications. The metallic nature of these films, representing a significant source of energy loss when they are subjected to high-frequency AC magnetic fields through the generation of eddy currents, was mitigated by the insertion of ultrathin insulating Al2O3 interlayers. Subsequent integration with thin-film piezoelectrics eliminated the reliance on bulk piezoelectric substrates and enables integration with Si-based electronics.

This work demonstrated the importance of interfacial engineering in the development of emerging magnetoelectric materials. A better understanding of the role that oxidation at the CoFeB/MgO interface plays in the electric-field control of magnetization in magnetic tunnel junctions has already contributed significantly to the field of spintronics. The insulated FeGa/NiFe multilayer composites serve as ideal candidates for incorporation into next-generation magnetoelectric antenna concepts.

Al-based materials, specifically aluminum oxide (Al₂O₃), aluminum nitride (AlN) and lithium aluminosilicate (Li_xAl_ySi_zO) were synthesized via atomic layer deposition (ALD) and investigated for their applications in power electronics and miniaturized Li-ion batteries.

Al₂O₃ and AlN films were deposited on two substrates, silicon carbide (SiC) and gallium nitride (GaN) based heterostructures, AlGaN/GaN, to compare their electrical performances as alternative dielectrics for wide bandgap semiconductor based power devices. Amorphous Al₂O₃ was deposited at 195-200 ^oC at a rate of 0.75-1 �/cycle. The film exhibited a dielectric constant of 9 and a leakage current of 10^-3 A/cm² at 8 MV/cm on SiC. When it was applied on AlGaN/GaN, the Al₂O₃ passivation resulted in an increased sheet carrier density but a dramatic decrease in the mobility compared to those of a clean AlGaN/GaN substrate. Crystalline AlN was deposited at 540 ^oC with a rate of 1.5 �/cycle. The AlN film demonstrated a dielectric constant of 8.3 and a leakage current density of 10^-3 A/cm² at 4.3 MV/cm on SiC. When AlN was applied on AlGaN/GaN, an increased carrier density was observed while the mobility was at 1130 cm²/V-s, similar to that of a clean AlGaN/GaN. The electrical properties of synthesized AlN were promising and comparable to those of MBE or sputtering synthesized AlN, confirming the promise of ALD for synthesizing AlN. Due to their material properties, Al₂O₃ is preferred choice for preventing gate leakage current on SiC, whereas AlN demonstrated superior capability of passivating AlGaN/GaN.

Stoichiometric LiAlSiO₄ was realized at 290 ^oC with a rate of ~23 �/global cycle, in which one global cycle sequence represented 10(Al-O)-6(Li-O)-4(Si-O) ALD cycles. As-deposited films were amorphous, pin-hole free, as confirmed by electrochemical testing in ferrocene, and conformal over 3D nanowires. The ionic conductivity of Li_xAl_ySi_zO films was 10^-9-10^-7 S/cm and the activation energy was 0.34-0.98 eV, both correlated to cation contents in the films. After rapid thermal annealing at 900 ^oC, the as-deposited LiAlSiO₄ films crystallized into epitaxial β-LiAlSiO₄ on Si (001) with a relationship of β-LiAlSiO4 (1 2bar 1 0) || Si (100) and β-LiAlSiO₄ (1 0 1bar 0) || Si (001). The application of the LiAlSiO₄ film on tin dioxide (SnO₂) NWs showed that the film possessed a high ionic conductivity, which suppressed the formation of metallic Sn particles, showing the capability of Li_xAl_ySi_zO films to serve as electrolytes and surface modification layers in 3D Li-ion microbatteries.

Multiferroics exhibit remarkable tunabilities in their ferromagnetic, ferroelectric and magnetoelectric properties that provide the potential in enabling the control of magnetizations by electric field for the next generation non-volatile memories, antennas and motors. In recent research and developments in integrating single-phase ferroelectric and ferromagnetic materials, multiferroic composite demonstrated a promising magnetoelectric (ME) coupling for future applications. Atomic layer deposition (ALD) technique, on the other hand, allows fabrications of complex multiferroic nanostructures to investigate interfacial coupling between the two materials.

In this work, radical-enhanced ALD of cobalt ferrite (CFO) and thermal ALD of lead zirconate titanate (PZT) were combined in fabricating complex multiferroic architectures in investigating the effect of nanostructuring and magnetic shape anisotropy on improving ME coupling. In particular, 1D CFO nanotubes and nanowires; 0D-3D CFO/PZT mesoporous composite; and 1D-1D CFO/PZT core-shell nanowire composite were studied. The potential implementation of nanostructured multiferroic composites into functioning devices was assessed by quantifying the converse ME coupling coefficient.

The synthesis of 1D CFO nanostructures was realized by ALD of CFO in anodic aluminum oxide (AAO) membranes. This work provided a simple and inexpensive route to create parallel and high aspect ratio (~55) magnetic nanostructures. The change in magnetic easy axis of (partially filled) CFO nanotubes from perpendicular to parallel in (fully-filled) nanowires indicated the significance of the geometric factor in controlling magnetizations and ME coupling.

The 0D-3D CFO/PZT mesoporous composite demonstrated the optimizations of the strain transfer could be achieved by precise thickness control. 100 nm of mesoporous PZT was synthesized on Pt/TiOx/SiO2/Si using amphiphilic diblock copolymers as a porous ferroelectric template (10 nm pore diameter) for ALD CFO growth. The increased filling of CFO decreased the mechanical flexibility of the composite for electric field induced strain, hence the converse ME coupling was mitigated. The highest converse ME coefficient of 1.2 10-5 Oe-cm/mV was achieved with a 33% pore filling of CFO, in compare to 1 � 10-5 Oe-cm/mV from mesoporous CFO filled with 3 nm of PZT in literature (Chien 2016).

Highly directional 1D-1D PZT-core CFO-shell composite in AAO demonstrated the magnetic shape anisotropy could be modulated. The CFO shell thickness allowed the tuning of magnetic easy axis and saturation magnetizations; whereas the PZT volume allowed the optimization of electric field induced strain of the composite. Enhanced converse ME coupling of 1.3 � 10-4 Oe-cm/mV was realized by 5 nm CFO shell on 30 nm of PZT core.

In summary, the work has demonstrated nanostructuring of multiferroic composite is an effective pathway to engineer converse ME coupling through optimizations of magnetic shape anisotropy and interfacial strain transfer.

A viable solid state inorganic Li-ion conductor, lithium aluminosilicate (LixAlySizO, LASO), was synthesized by atomic layer deposition (ALD). Investigations of the reaction mechanisms during ALD depositions of the constituent oxides of LASO, Al2O3, LiOH, and SiO2, were first conducted via in-situ Fourier transform infrared spectroscopy (FTIR). The deposition rate of ALD Al2O3 and LiOH were 1.1 and 1.2 Å/cycle respectively while it was not possible to deposit SiO2 by ALD at the conditions studied. The growth of three tertiary oxides, AlxSiyO, LixAlyO, and LixSiyO were confirmed by ALD, demonstrating that functionalization through hydroxylated LiOH and Al2O3 surfaces enabled the incorporation of ALD SiO2 at low temperatures. The in-situ FTIR study revealed that presence of electropositive metal atom in vicinity of surface Si-OCH2CH3* specie is essential for the incorporation of ALD SiO2 at low temperatures. No presence of incubation times were found for ALD deposition of each constituent oxide on the other, allowing ALD deposition LASO as a solid solution based on its constituent oxides. The growth rate of ALD LiAlSiO4 was found to be 20.6 Å/global cycle.

The as-deposited ALD LASO films were amorphous with desired physiochemical properties viable for solid electrolyte applications. The calculated values of ionic conductivity were in the range of 1.75 × 10-9 to 7.22 × 10-8 S/cm, which were tunable by adjusting the number of ALD sub-cycles of the constituent oxides. The activation energy of Li-ion conduction was found to be between 0.46-0.89 eV, which was comparable to that reported in literature. An epitaxial crystallization of the as-deposited amorphous films into β-LiAlSiO4 was achieved for selected compositions of LASO upon post-deposition rapid thermal annealing, with a relationship of LiAlSiO4 || Si (100) and β-LiAlSiO4 || Si (001) to Si substrate. An exceptional conformality of ALD LASO coating was demonstrated on prospective 3D architectures for electrodes, including high aspect ratio trenches and nanowires.

Integration of ALD LixAlySizO films with electrode materials including carbon electrode (both 2D and 3D), SnO2, and SiGe nanowires were investigated. ALD LixAlySizO coating on 2D carbon electrode improved the coulombic efficiency from 91% to 98%. Integration of 3D carbon array electrodes demonstrated a high areal capacity of 7.36 mAh/cm2, which was 6.75 times higher than the maximum areal capacity obtained from 2D carbon electrodes. In-situ HRTEM study on ALD coated SnO2 and Si0.6Ge0.4 nanowires demonstrated promising prospects of ALD LASO not only as a solid electrolyte but also as a stable artificial solid electrolyte interface layer which can improve both physiochemical and mechanical stability of electrode materials.

Complex metal oxides exhibit remarkable tunability in their ferromagnetic, ferroelectric, and multiferroic properties that enable future applications such as non-volatile memory, miniaturized antenna, sensors and actuators. Motivated by the promise of high magnetoelectric coupling from nanostructured multiferroics, atomic layer deposition (ALD) processes were developed to synthesize single-phase ferroics that would be further integrated to form composite multiferroics. The highly conformal ALD coatings promised intimate interfaces of the various ferroic phases to realize tunable magnetoelectric coupling.

In this work, a radical enhanced ALD process was used to synthesize the complex oxide nanostructures, using metalorganic precursors Y(tmhd)3 (tmhd = 2,2,6,6-tetramethylheptane-3,5 dione), Mn(tmhd)3, Bi(tmhd)3, Co(tmhd)2, and Fe(tmhd)3 as well as oxygen atoms produced from a microwave powered atomic beam source. The processing-structure-property relations were systematically studied for three material systems: YMnO3 (YMO), BiFeO3 (BFO), and CoFe2O4 (CFO). For YMO, it was found that the crystal structure forming between orthorhombic or hexagonal configurations was due to the substrate and that Si(111) and Y:ZrO2 (111) substrates preferentially formed the orthorhombic and hexagonal phases respectively. The magnetic susceptibility versus temperature of YMO was characterized and it was determined that the magnetic anomalies at ~48 K and ~80 K corresponded to orthorhombic and hexagonal phases respectively which matched the reports given from literature. The ALD BFO films were grown on SrTiO3 (STO) (001) substrates and were found to crystallize epitaxially in the (001) pseudocubic orientation when annealed at 650 °C. The ferroelectric properties were confirmed via PFM while the weak ferromagnetic coupling showed a magnetic saturation (Ms) of approximately 27 emu/cm3. The ALD CFO films were grown on STO (001) substrates and were mostly polycrystalline with a textured (001) orientation. The magnetic properties were studied and the Ms ranged from 260 to 550 emu/cm3 and the magnetic coercivity (Hc) ranged from 200 to 2180 Oe depending on the direction of the magnetic field, annealing condition, and thickness which matched values of those found in bulk and other thin film studies.

Synthesis of multiferroic composites with nanostructure was enabled by ALD. 2-2 multiferroic composite configurations using BiFeO3 and CoFe2O4 were synthesized by ALD and it was determined that for 40 nm thick films, a change in the easy axis of magnetization could be controlled by changing the size and number of repeating BFO/CFO bilayers. 0-3 multiferroic composite configurations using both BFO/CFO and CFO/PZT were synthesized by a hybrid approach first using evaporation induced self-assembly to deposit a porous metal oxide thin film followed by the ALD film. It was confirmed by SEM that the ALD coating was conformal and the magnetic properties were studied. The CFO template film with ALD BFO was found to have an Ms of 151.1 emu/cm3 out-of-plane and 89.4 emu/cm3 in-plane while Hc was about 2.0 kOe for both orientations. For the PZT template film with CFO overlayer, it was found that the Ms began to saturate at about 40-45 emu/cm3 once the CFO thickness exceeded 4 nm due to the restricted pore necks. These volumetric values exceeded thin films found in literature with 0-3 configurations that were synthesized using wet techniques.