Thin Crystalline Layers Research Articles

The oxidation-dissolution behavior of Cr-coated Zr alloy in high temperature water

The corrosion and dissolution behavior of Cr-coated Zr alloy were investigated in high temperature water under varying dissolved oxygen (DO) and temperatures. Results demonstrate that the oxidation and dissolution rates of Cr coatings increase significantly with higher DO levels and temperature, while the Zr substrate remains unaffected by DO concentration. At DO levels below 10 ppb, Cr coatings exhibit high stability, but at 300 ppb DO, rapid corrosion/dissolution and spallation occur. The electrochemical potential (ECP) shifts in response to temperature and DO, driving the dissolution mechanism through three distinct region: steady-state, field-assisted dissolution (FAD), and complete dissolution. During the FAD period, a porous nanocrystalline Cr2O3 layer with residual Cr forms, characterized by non-uniform dissolution due to preferential oxidation at grain boundaries and microstructural defects. The soluble HCrO4− ions form at the base of the porous layer, followed by partial recrystallization at the surface, leading to the development of a thin Cr2O3 crystalline layer.

Conformal growth of GaP on high aspect ratio Si structured surface via plasma-enhanced atomic layer deposition

This article is concerned with the study of conformal growth of thin gallium phosphide (GaP) layers by plasma-enhanced atomic layer deposition (PE-ALD) on a Si structured surface. GaP layers were deposited on (100) silicon wafers with a structured surface in the form of silicon microcolumns and black silicon. Deposition process were carried out at temperature of 380 °C using trimethylgallium and phosphine precursors. According to transmission electron microscopy (TEM), GaP layers deposited by this method conformally grown on the high aspect ratio structured silicon surface. The energy-dispersive X-ray spectroscopy (EDX) study show that the distribution of the main components of the GaP layer is uniform alongside surface of the silicon microcolumns and wires. High resolution TEM study confirms that GaP layers on the surface of silicon microcolumns and wires are epitaxial with the inclusion of twin lattice defects. Therefore, this deposition method can be used for the conformal deposition of thin crystalline layers of GaP on structured silicon surfaces with a high aspect ratio.

(Invited) Sequential 3D Integration of Ge Transistors on Si CMOS

In order to keep the scaling progress going is to go 3D. This paper outlines some technology challenges and solutions to integrate Ge p-type MOSFETs sequentially on Si CMOS. Such a solution addresses the grand challenge to enable increased device density. However, the device itself does not have to scale but at the same time innovative solutions are suggested for low supply voltage operation enabling energy efficient integrated circuits (ICs) that will not be dominated by energy consumption in interconnects.By stacking the transistors on top of each other, and connect them with inter-tier via, the density of transistors per unit area increases. This approach demands that transistors are fabricated at a lower temperature compared to today’s Si CMOS technology. Therefore, we have focused on Ge based transistors, which has an inherently lower process temperature compared to Si transistors.In this paper several technological and design breakthroughs towards realizing Ge based sequential 3D circuits will be shown. We will present: A process to realize thin single crystalline Ge layers on planarized wafers with metal layers in lower tiers.A gate dielectric stack (Ge/Si/TmSiO/Tm2O3/HfO2/TiN) on Ge that enables adequately low defect densities at the dielectric/Ge interface allowing predictable and reliable Ge transistorsFully depleted Ge pFET devices fabricated at a low temperature compatible with sequential 3D. The devices exhibits 60% higher mobility compared to reference Si devices.3D digital circuits with pFETs on top of nFETs can enable area reduction by 30-50% depending on cell type.3D standard cells with lower parasitic capacitance (~30%) compared to 2D cells, enabling lower dynamic power consumption and more energy efficient integrated circuits.

In Situ Intrinsic Self-Healing of Low Toxic Cs2 ZnX4 (X=Cl, Br) Metal Halide Nanoparticles.

This study reports on the intrinsic and fast self-healing ability of all inorganic, low-toxic Cs2 ZnX4 (X=Cl, Br) metal halide nanoparticles (NPs) when subjected to local heating by electron beam irradiation in high-resolution transmission electron microscopy (HR-TEM). The local heating induces the creation of nanoshells (NSs) following the template of the corresponding NPs, which are subsequently healed back to their original state within several minutes. Energy dispersive spectroscopy (EDS) and fast Fourier transform (FFT) analysis reveal that the composition, phase, and crystallographic structure of the original NPs are restored during the self-healing process, with a thin crystalline layer observed at the bottom of the NSs acting as the healing template. The inelastic scattering of the electron beam energy generates local heat that causes rapid atomic displacement, resulting in atomic mobility that lowers the density of the material and leads to NSformation. A unique insitu TEM heating stage measurement demonstrates the appearance of identical damage and self-healing to those induced by the electron beam. The NPs exhibit excellent stability under ambient conditions for up to a month, making them suitable for self-healing scintillators and other optoelectronic applications that require atomic-scale stability and healing.

Anodization Time Effect on Silver Particles Deposition on Anodic Oxide Coating over Al Produced by Plasma Electrolytic Oxidation

In this study, 6061 Al alloy was galvanostatically anodized under the Plasma Electrolytic Oxidation (PEO) condition. A factorial design of 22 was carried out using two variables (anodization time and presence of silver in the electrolyte) on two levels, i.e., 20 and 60 min of anodization and the absence/presence of silver ions in the electrolyte. The Al anodization was performed in sodium silicate electrolyte, applying a constant current density of 20 mA cm−2. The oxide characterization was performed by Scanning Electron Microscopy (SEM), surface roughness analysis (RMS), Energy Dispersive Spectroscopy (EDS), Rutherford Backscattered Spectroscopy (RBS), and Grazing Incidence X-ray Diffraction (GIXRD). The SEM micrographs revealed an irregular porous structure with cracks on the oxide surface composed of a thin crystalline layer of γ-Al2O3 over the Al substrate. From EDS and RBS analysis, it was possible to identify the elements Al, O, Si, Ag, and Na, demonstrating that a shorter anodization time (20 min) led to a significant amount of silver deposits on the outer layer of the oxide coating, mainly deposited in the surroundings of the pores. Conversely, the silver content on the PEO film anodized for 60 min was meager. These results demonstrated that the anodization time was the critical control variable for the amount of silver deposited over the oxide film. The shorter the anodizing time, the higher the silver content on the PEO coating.

Molecular Dynamics Investigation of the Effect of the Interface Orientation on the Intensity of Titanium Dissolution in Crystalline and Amorphous Aluminum

The influence of the interface orientation on the intensity of dissolution of titanium in crystalline and amorphous aluminum is studied by molecular dynamics simulation. The following four orientations of the Ti–Al interface with respect to the Ti (hcp) and Al (fcc) lattices are considered: (1) (0001):(111), (2) (0001):(001), (3) (101¯0101¯0):(111), and (4) (101¯1101¯1):(001). The interface orientation is found to influence the intensity of dissolution of titanium in aluminum, which increases for the accepted designations in the order 1–2–3–4. An important phenomenon in this case turns out to be the formation of a thin (2–3 atomic planes thick) crystalline layer in aluminum, which repeats the crystal lattice of titanium, at the initial stage of dissolution. At a temperature below the melting point of aluminum, a grain boundary parallel to the interface forms behind this layer. At temperatures above the melting point of aluminum, this crystalline layer is preserved, but its thickness decreases gradually as the temperature increases. For aluminum in an amorphous state at temperatures below its melting point, the dissolution of titanium occurs at almost the same intensity as in the crystalline state of aluminum, which is explained by the formation of a similar crystalline layer in aluminum at the interface in all cases.

Polymorphic crystalline wetting layers on crystal surfaces

Analogous to surface premelting, we show that a crystal surface can undergo a pre-solid–solid transition. This means that it develops a thin polymorphic crystalline layer before reaching the solid–solid transition temperature if two crystals can form a low-energy coherent interface. We confirm this in simulations and colloid experiments at single-particle resolution. The power-law increase of surface layer thickness is analogous to premelting. Different kinetics and reversibilities of surface-crystal growth are observed in various systems. Surface crystals exist not only under thermal equilibrium but also during melting, crystallization and grain coarsening. Furthermore, the premelting and pre-solid–solid transition can coexist, resulting in double surface wetting layers. We hypothesize that such surface phenomena also exist in some atomic and molecular crystals, and this could provide a mechanism to tune the properties of the materials.

Maximum Power of Thin-Film Capacitive Electrostatic Micromotors Based on Nanogaps

This paper is devoted to the determination of the value of the maximum specific power of capacitive electrostatic micromotors based on nanometer working gaps. The motors under consideration were developed earlier. They have the following structure: a metal—thin crystalline ferroelectric layer with a high dielectric constant—a nanometer working gap—a movable electrode. The mechanism limiting the magnitude of the maximum field in the gap have also been determined in previous works. The mechanism is the stripping of atoms from the surface of the movable electrode under the action of electrostatic forces. It was shown that the maximum energy density in the working gap can be as high as 1.6 × 109 J/m3. In the presented paper, a maximum frequency of electromechanical energy conversion as high as 10 MHz is estimated for these motors, with a maximum specific power of 5 × 108 W/kg. The application of the proposed motors for micromachines is discussed.

Structural Properties of TaAs Weyl Semimetal Thin Films Grown by Molecular Beam Epitaxy on GaAs(001) Substrates

Thin crystalline layers of TaAs Weyl semimetal are grown by molecular beam epitaxy on GaAs(001) substrates. The (001) planes of the tetragonal TaAs lattice are parallel to the GaAs(001) substrate, but the corresponding in-plane crystallographic directions of the substrate and the layer are rotated by 45°. In spite of a substantial lattice mismatch (about 19%) between the GaAs(001) substrate and TaAs epilayer, no misfit dislocations are observed at the GaAs(001)/TaAs(001) interface. Only stacking fault defects in TaAs are detected by transmission electron microscopy. Thorough X-ray diffraction measurements and analysis of the in situ reflection high-energy electron diffraction images indicate that TaAs layers are fully relaxed already at the initial deposition stage. Atomic force microscopy imaging reveals the columnar structure of the layers, with lateral (parallel to the layer’s surface) columns about 20 nm wide and 200 nm long. Both X-ray diffraction and transmission electron microscopy measurements indicate that the columns share the same orientation and crystalline structure.

(Invited, Digital Presentation) Approach to Neuromorphic Computing with Ferroelectric Schottky Barrier FETs

Neuromorphic computing inspired by neural network systems of the human brain enables energy efficient computing as a solution of the von Neumann bottleneck. A neural network consists of thousands or even millions of neurons which communicate with each other through connected synapses. Synapses can memorize and process the information simultaneously. The plasticity of a synapse to strengthen or weaken its activity over time make it be capable of learning and computing. Thus, artificial synapses which can emulate functionalities and the plasticity of bio-synapses form the backbone of a neuromorphic computing system.Non-volatile memories with two-terminals, like resistive random-access memory (ReRAM), phase change memory (PCM), are attractive candidates for artificial synapses. However, signal processing and learning cannot be performed simultaneously in these two-terminal synapses. FeFET, similar to a MOSFET structure using CMOS compatible HfO2 based ferroelectrics as gate oxide forms three-terminal synapses offering high endurance, good performance and high energy efficiency. In contrast to two-terminal devices, three terminal FeFET based synapses can perform processing and learning at the same time. In order to maintain the ferroelectric properties of an HfO2 based ferroelectric film, high temperature annealing should be avoided after the ferroelectric layer deposition. In this paper, we present ferroelectric NiSi2 source/drain Schottky barrier (SB) MOSFET (FE-SBFET) structure (Fig.1a), which requires neither ion implantation nor thermal activation of source/drain contacts at high temperatures.FE-SBFETs were fabricated on SOI substrates with a boron-doped (1016 B/cm-3), 55 nm thick top Si layer and a 145 nm thick buried oxide (BOX) layer. Very thin (9 nm) single crystalline NiSi2 layers which offer superior properties of uniform and stable SB contacts on Si are used at source/drain regions. A gate stack consisting of 10 nm thick Hf0.5Zr0.5O2 (HZO) layer and a 40 nm thick TiN layer are deposited by ALD and sputtering, respectively. A rapid thermal annealing at 500 °C is performed to crystallize the HZO into a ferroelectric phase before the gate patterning. The fabricated device has a channel length of 10 µm and a gate width of 10 µm. The overlap between the top gate and NiSi2 is 6 µm along the channel and 10 µm wide on each side. The ferroelectric polarization modulates both the SB at the source/drain contacts as well as the potential in the channel, thus changing the carrier injection through the SB. The Id-Vg transfer characteristics of a p-type FE-SBFET shows a clockwise hysteresis which is caused by the ferroelectric polarization switch.The excitatory post-synaptic current (EPSC), one of the typical short-term synaptic plasticity features for biologic synapses, is characterized by measuring the transient drain currents for a voltage pulse on the gate of a FE-SBFET (Fig.1b). The amplitude of the pulse VAM changes from -0.2 to -1.2 V with a fixed pulse width tpw=1 μs. We found that the EPSC peak value increases linearly with VAM. It shows a very low energy/spike consumption of 2fJ/spike at VAM=-0.2 V, demonstrating a very high energy efficiency. From the EPSC measurements with repeated gate voltage pulses paired-pulse facilitation/depression (PPF/PPD) are characterized showing an exponential decay, similar to biological synapses.The long-term synaptic plasticity of FE-SBFET synapses is characterized by a series repeated identical or non-identical pulses. The later can improve the long-term potentiation/depression (LTP/LTD) symmetry and linearity. The measurements show a large Gmax/Gmin ratio, very high endurance and small cycle-to-cycle (CTC) variation (1.06%) due to the perfect contact of NiSi2 (Fig.1c). The biological neuron-like spike-timing-dependent plasticity (STDP) is characterized for the FE-SBFET synapse. The results show an asymmetric anti-Hebbian STDP, which is one of the biological STDP functionalities (Fig.1d).In conclusion, the fabricated FE-SBFET synapse exhibits multiple synaptic functions with high endurance and small variations. The ultra-low energy/spike consumption indicates a high potential for low power neuromorphic computing applications. Acknowledgement: This work was supported by the Federal Ministry of Education and Research (BMBF, Germany) in the project NEUROTEC (16ME0398K). Figure 1

Near-infrared emission in Er- and Pr-doped YSZ crystalline superlattices

Broadband on-chip light amplifier is one of the key building blocks for the development of integrated circuits for datacom and telecom applications. In this context, the article reports on the near-IR emission properties of rare-earth doped crystalline thin layers of Y2O3–ZrO2 (YSZ): Er-doped YSZ, Pr-doped YSZ and a superlattice of Er- and Pr-doped YSZ. Absorption studies proved differences in wavelengths in superlattice sample with Pr3+ and Er3+ in comparison with Er-doped YSZ and Pr-doped YSZ monolayers. Power efficiency was determined for all samples, revealing larger emission and higher optical efficiency for Er3+ ions at 1530 nm (C-band) than Pr3+ emission at 1350 nm (O-band) in the superlattice sample. Simultaneous emission from Er3+ and Pr3+ ions was observed by exciting the Er- and Pr-doped YSZ superlattice in a range from 980 to 1000 nm wavelengths. Besides, energy transfer from Pr3+ to Er3+ was demonstrated in the superlattice sample containing Pr3+ and Er3+ ions.

Study of recrystallization and activation processes in thin and highly doped silicon-on-insulator layers by nanosecond laser thermal annealing

A thorough study of the phosphorus (P) heavy doping of thin Silicon-On-Insulator (SOI) layers by UV nanosecond Laser Thermal Annealing (LTA) is presented in this work. As a function of the implant dose and laser annealing conditions, the melting regimes and regrowth processes, as well as the redistribution and activation of P in the top-Si amorphized layer, were investigated. The findings emphasize the critical role of the thin crystalline silicon layer that remains after the top-Si layer amorphizes, as it provides nucleation seeds for liquid phase recrystallization. The effect of the implant dose on the recrystallization process is thoroughly investigated in terms of melt energy thresholds, crystallographic nature of the resolidified layer, defect formation, surface roughness, and the formation of hillocks on the silicon surface. Optimized laser annealing conditions, corresponding to the laser energies just preceding the onset of the full melt, were identified for all implanted doses. Such optimized layers have perfect crystallinity, negligible P out-diffusion, a nearly perfectly flat P depth profile located below the segregation-induced surface pileup peak, and dopant active concentrations well above 1021 cm−3, which is close to the highest reported values for phosphorus in bulk Si substrates.

Сomposition, structure and functional properties of silver-tungsten composition electrochemistry coatings formed with the help of ultrasound

Influence of electrolyte composition and deposition parameters on the composition, structure, physicalmechanical and functional properties of composite silver-tungsten coatings was studied. It was shown that addition of sodium tungstate in electrolyte and application of ultrasound at the electroplating leads to formation of silver layers that contains tungsten oxides and demonstrates lower crystalline nucleus. Application of ultrasound vibration at the electrochemical deposition increases ability for plating process control and allows to optimize electrophysical and functional properties of composite electrochemical coatings, to make dense fine crystalline thin layers. Obtained layers demonstrate increased microhardness (by 10–50 %), wear resistance (1,5–2 times), corrosion resistance and improved contact electrical resistance. It is shown that application of ultrasound effect to electrodeposition allows increased level of permissible current density and provides.

Manipulation of optical properties in thin tetradymite layers

Thin Bi2Se3 layers are promising material for many optical and optoelectronic applications. In this work, thin crystalline layers of Bi2-chalcogenides were deposited on highly cleaned glass substrates by vacuum thermal evaporation technique. The optical properties of the concerned layers were investigated with ultraviolet–visible-near infra-red (UV–Vis–NIR) spectra. The effect of thickness reduction and the annealing treatment have been studied. Thinning the film to few nanometers resulted in a significant enhancement of light transmission through the prepared materials. Also, simultaneous reduction of layer's thickness and annealing treatment significantly improved the optical transmission. Such transmissivity enhancement opens avenues for transparent electrode applications.

Formation of structure of TiNiCu alloys with high copper content upon producing by planar flow casting

The rapidly quenched alloys of the quasibinary intermetallic TiNi-TiCu system with a high copper content (more than 25 at.%) are of great interest as shape memory materials due to the possibility of a significant decrease in the temperature and deformation hysteresis in comparison with the binary TiNi alloy. To obtain alloys with a copper content of 25 to 40 at.%, the planar flow casting technique was used. The alloys were fabricated at a melt cooling rate of about 106 K/s in the form of ribbons 30-50 μm thick and wide in the range from 7 to 20 mm. The study of the structure of the alloys was carried out using X-ray diffraction analysis, scanning and transmission electron microscopy. It was shown that from the ribbon side, contacting the quenching wheel, all alloys are amorphous, while on the non-contact side of the ribbons of alloys with 25 and 30 at.% Cu, a thin surface crystalline layer with a B2 structure is observed. Using energy dispersive X-ray spectroscopy, it was found that the content of the alloy components in the amorphous and crystalline phases coincides.

Higher-order topological insulators in amorphous solids

We identify the possibility of realizing higher order topological (HOT) phases in noncrystalline or amorphous materials. Starting from two and three dimensional crystalline HOT insulators, accommodating topological corner states, we gradually enhance structural randomness in the system. Within a parameter regime, as long as amorphousness is confined by outer crystalline boundary, the system continues to host corner states, yielding amorphous HOT insulators. However, as structural disorder percolates to the edges, corner states start to dissolve into amorphous bulk, and ultimately the system becomes a trivial insulator when amorphousness plagues the entire system. These outcomes are further substantiated by computing the quadrupolar (octupolar) moment in two (three) dimensions. Therefore, HOT phases can be realized in amorphous solids, when wrapped by a thin (lithographically grown, for example) crystalline layer. Our findings suggest that crystalline topological phases can be realized even in the absence of local crystalline symmetry.

Efficiency improvement of flexible Sb2Se3 solar cells with non-toxic buffer layer via interface engineering

Thin film Sb2Se3 solar cells have gained a worldwide attention as a highly potential Earth-abundant photovoltaic technology. While Sb2Se3 solar cells are typically fabricated in superstrate structure, substrate configuration devices offer versatility in substrate material choice particularly important for flexible devices. However, all substrate type Sb2Se3 solar cells use CdS as a buffer layer synthesized by chemical bath deposition method, during which Sb2Se3 surface is degraded limiting solar cell performance. Additionally, contamination layer has been reported to exist on Sb2Se3 surface after deposition under low vacuum conditions. In this study, we demonstrate a facile strategy to improve Sb2Se3 solar cell power conversion efficiency (PCE) by replacing CdS with In2S3 and applying a two-step treatment involving chemical etching and subsequent annealing. We show that a combined treatment which first removes the contamination layer and then passivates interface defects improves PCE more than three-fold, from 1.6% to 5.35%. Effective passivation of interface defects is ascribed to the formation of thin crystalline Sb2O3 layer on Sb2Se3 absorber surface after the treatment. In conclusion, optimized two-step treatment offers a simple and effective way to improve PCE and replacement of toxic CdS with In2S3 demonstrates new device design options towards flexible and non-toxic Sb2Se3 solar cells.

Forming Si nanocrystals on insulator by wet anisotropic etching

Implementing the Silicon-On-Insulator platform, we reveal an approach to fabricate Si nanocrystals on insulator by a single step, wet anisotropic etching of thin crystalline layers. The evolution of the Si layer was investigated from the onset of the dissolution process up to the development of isolated nanocrystals. Our results also provide several insights into the understanding of the early stages of the hillocks formation characteristic for the anisotropic etching of Si(001). We discuss several related mechanisms and we give experimental evidences that support the stabilization of the pyramidal hillocks apices by short-lived silicate particles.

Combining super-resolution microscopy with neuronal network recording using magnesium fluoride thin films as cover layer for multi-electrode array technology

We present an approach for fabrication of reproducible, chemically and mechanically robust functionalized layers based on MgF2 thin films on thin glass substrates. These show great advantages for use in super-resolution microscopy as well as for multi-electrode-array fabrication and are especially suited for combination of these techniques. The transparency of the coated substrates with the low refractive index material is adjustable by the layer thickness and can be increased above 92%. Due to the hydrophobic and lipophilic properties of the thin crystalline MgF2 layers, the temporal stable adhesion needed for fixation of thin tissue, e.g. cryogenic brain slices is given. This has been tested using localization-based super-resolution microscopy with currently highest spatial resolution in light microscopy. We demonstrated that direct stochastic optical reconstruction microscopy revealed in reliable imaging of structures of central synapses by use of double immunostaining of post- (homer1 and GluA2) and presynaptic (bassoon) marker structure in a 10 µm brain slice without additional fixing of the slices. Due to the proven additional electrical insulating effect of MgF2 layers, surfaces of multi-electrode-arrays were coated with this material and tested by voltage-current-measurements. MgF2 coated multi-electrode-arrays can be used as a functionalized microscope cover slip for combination with live-cell super-resolution microscopy.

Evolution of Phosphorene Sheets through Direct Crystallization of Thin‐Film Red Phosphorus

A novel hydrogen plasma treatment to convert an amorphous phosphorus film deposited on silicon substrates into a thin crystalline layer is successfully developed. The amorphous phosphorus layer is deposited on desired substrates as silicon using vacuum evaporation in a direct‐current plasma reactor in a controllable fashion. The formation of 2D phosphorene layers is based on the phase transition of a previously deposited amorphous film into the crystalline black phosphorus flakes. Direct transformation from red phosphorus to black can be achieved at a temperature of 300 °C on desired substrates as silicon, although mica and glass can also be used. This allotrope transformation can be achieved without any high pressure or high temperature. Apart from hydrogen plasma treatment, ultraviolet (UV) exposure to see any possible improvement in the 2D layer formation is also used herein. Various characterization techniques including scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and Raman spectroscopy are used to study the crystallinity and morphology of the samples. In addition, the plasma‐treated flakes are used to realize photodetectors which show excellent response to illuminating light. While the hydrogen plasma treatment leads to crystalline phosphorene sheets, the UV treatment results in granular and partially crystalline nanostructures.