Mikko Nisula

This work reports on the atomic layer deposition process combining lithium hexamethyl disilazide (LiHMDS) and trimethylphosphate (TMP), and studies the impact of adding a trimethylaluminum (TMA) pulse to this process. When only minute traces of aluminum are incorporated, the deposited layer becomes amorphous instead of crystalline. The TMA–TMP interaction plays a key role in this process and is revealed by time-resolved full-range quadrupole mass spectrometry. It is hypothesized that the interaction of unreacted –OCH₃ groups with TMA and the formation of Li₄P₂O₇ units lead to higher growth and structural changes as compared to the phosphate process without TMA. The conformal deposition of lithium-containing phosphates may find applications in modification of electrode–electrolyte interfaces in lithium-ion batteries. This is demonstrated in a half-cell. The amorphous mix of Li₄P₂O₇ and Li₃PO₄ units in the films grown with TMA benefits the conductive properties of the material: an ionic conductivity of 1.47 ± 0.09 × 10⁻⁷ S cm⁻¹ at 30 °C is achieved, with an activation energy 0.58 ± 0.02 eV.

Controlled surface functionalization with azides to perform on surface “click chemistry” is desired for a large range of fields such as material engineering and biosensors. In this work, the stability of an azido-containing self-assembled monolayer in high vacuum is investigated using in situ Fourier transform infrared spectroscopy. The intensity of the antisymmetric azide stretching vibration is found to decrease over time, suggesting the degradation of the azido-group in high vacuum. The degradation is further investigated at three different temperatures and at seven different nitrogen pressures ranging from 1 × 10^–6 mbar to 5 × 10^–3 mbar. The degradation is found to increase at higher temperatures and at lower nitrogen pressures. The latter supporting the theory that the degradation reaction involves the decomposition into molecular nitrogen. For the condition with the highest degradation detected, only 63% of azides is found to remain at the surface after 8 h in vacuum. The findings show a significant loss in control of the surface functionalization. The instability of azides in high vacuum should therefore always be considered when depositing or postprocessing azido-containing layers.

The prospect of introducing tunable electric conductivity in metal–organic coordination polymers is of high interest for nanoelectronic applications. As the electronic properties of these materials are strongly dependent on their microstructure, the assembly of coordination polymers into thin films with well-controlled growth direction and thickness is crucial for practical devices. Here, we report the deposition of one-dimensional (1D) coordination polymer thin films of N,N′-dimethyl dithiooxamidato-copper by atomic/molecular layer deposition. High out-of-plane ordering is observed in the resulting thin films suggesting the formation of a well-ordered secondary structure by the parallel alignment of the 1D polymer chains. We show that the electrical conductivity of the thin films is highly dependent on their oxidation state. The as-deposited films are nearly insulating with an electrical conductivity below 10^–10 S cm^–1 with semiconductor-like temperature dependency. Partial reduction with H₂ at elevated temperature leads to an increase in the electrical conductivity by 8 orders of magnitude. In the high-conductance state, metallic behavior is observed over the temperature range of 2–300 K. Density functional theory calculations indicate that the metallic behavior originates from the formation of a half-filled energy band intersecting the Fermi level with the conduction pathway formed by the Cu–S–Cu interaction between neighboring polymer chains.

Alucones are one of the best-known films in the Molecular Layer Deposition (MLD) field. In this work, we prove that alucone/Al ₂ O ₃ nanolaminate synthesis can be successfully performed by alternating alucone MLD growth with static O ₂ plasma exposures.

Artificial neural networks have revolutionized the field of artificial intelligence with human-like performance in fields such as computer vision and speech recognition. As the tasks for AI are increasingly demanding, significant gains in terms of speed and power consumption could be achieved by moving from software-based AI-systems to neuromorphic hardware that directly emulates the functionality and interconnectivity of the biological neural networks with layers of artificial neurons connected to each other via synaptic elements characterized by a weight factor. However, purely CMOS-based neuromorphic circuits are ultimately impractical for the implementation of large networks, as mimicking the operation dynamics and behavior of even a single synapse or neuron can take tens of transistors each to implement. Therefore, a key challenge is to develop new types of hardware, that is capable of achieving directly the in-memory processing of brain-like computation. For instance, single-element synapses can be achieved with memristors, in which the synaptic weight is emulated by their history-dependent variable conductance. Typically, various inorganic materials have been employed for these resistive switching devices that rely on the formation/dissolution of a conductive filament within an insulating matrix. The main challenges are the device-to-device and cycle-to-cycle variability caused by the stochastic nature of the filament formation. Additionally, the typically high conductance in the ON-state results in high energy consumption. Here we explore metal-organic coordination polymers deposited by atomic/molecular layer deposition (ALD/MLD) as an interesting alternative for this challenge. The most attractive feature of coordination polymers is their unparalleled tunability towards different functionalities arising from practically limitless number of metal and ligand combinations available. Yet, poor processability restricts their applicability towards nanotechnology applications. However, MLD, an extension to ALD, expands the deposition of thin films with superior quality to hybrid organic-inorganic materials with the implementation of volatile organic molecules as the co-reactant. We show that in high-quality coordination polymer thin films, post-synthetic control of their oxidation state is akin to tuning the doping level in terms band structure, and allows for tunable conductivity spanning over 8 orders of magnitude (10^-10 – 10^-2 S cm^-1). On device level, this redox-reaction based operation can be harnessed for low variability as the switching voltage is governed by the materials’ intrinsic reduction potential in contrast to the stochastic filament formation of the inorganic counterparts. Aside from the analog conductance tuning, the redox reaction rate, and thus rate of change in the device conductance is dependent on the excitation frequency and amplitude, thereby emulating the time-dependent dynamics of biological synapses such as spike-rate and spike timing dependent plasticity (SRDP and STDP). As the redox-reaction is also coupled with the motion of an associated counter ion, the interplay of the electron and ion mobilities apparently allows for the realization of concurrent short- and long-term memory in a single device. As such, ALD/MLD enabled coordination polymer thin films are attractive for use in more bio-realistic AI technology such as spiking neural networks.

This work demonstrates the possible usages of indium tin oxide (ITO) thin‐films as multifunctional coatings on V₂O₅ model electrodes for lithium‐ion batteries (LIBs). The thin films are produced with the atomic layer deposition (ALD) method via adjusting the ratio of In₂O₃ and SnO₂ sub‐layers to a well‐controlled In: Sn contents. The highest conductivity value (7.37 × 10⁻⁴ Ω cm) of as‐grown ITO film is obtained from the sample containing 5% SnO₂ of overall ALD cycles. The ITO thin‐films are further investigated as multifunctional coatings on ALD V₂O₅ electrodes for LIBs: At first, dual electronic and ionic conductive protecting properties of ITO layer are explored to attenuate the fading of the battery capacity by improving the cycling stability. Second, the feasibility of ITO layer as a dual functioning current collector‐cum‐protective coating layer is demonstrated. Third, ITO layer is investigated as a current collector and display performance comparable to that of Pt as current collector of traditional thin‐film LIBs. The electronic and electrochemical properties of ITO provide the opportunity to use ITO as a multifunctional coating for (3D) thin‐film LIBs and can find potential usages in miniaturized electronic devices.