Local Anodic Oxidation Research Articles

Anisotropic Effects in Local Anodic Oxidation Nanolithography on Silicon Surfaces: Insights from ReaxFF Molecular Dynamics.

Fully understanding the anisotropic effect of silicon surface orientations in local anodic oxidation (LAO) nanolithography processes is critical to the precise control of oxide quality and rate. This study used ReaxFF MD simulations to reveal the surface anisotropic effects in the LAO through the analysis of adsorbed species, atomic charge, and oxide growth. Our results show that the LAO behaves differently on silicon (100), (110), and (111) surfaces. Specifically, the application of an electric field significantly increases the quantity of surface-adsorbed -OH2 while reducing -OH on the (111) surface, and results in a higher charge on a greater number of Si atoms on the (100) surface. Moreover, the quantity of surface-adsorbed -OH plays a pivotal role in influencing the oxidation rate, as it directly correlates with an increased formation rate of Si-O-Si bonds. During bias-induced oxidation, the (111) surface appears with a high initial oxidation rate among three surfaces, while the (110) surface underwent increased oxidation at higher electric field strengths. This conclusion is based on the analysis of the evolution of Si-O-Si bond number, surface elevation, and oxide thickness. Our findings align well with prior theoretical and experimental studies, providing deeper insights and clear guidance for the fabrication of high-performance nanoinsulator gates using LAO nanolithography.

Creation and Characterization of Nanoscale Ribbons on MoS2 by Atomic Force Microscope Nanolithography

The atomic force microscope (AFM) has been widely used for fabricating the nanoscale oxide ribbons on various materials surface. Herein, we first conducted local anodic oxidation (LAO) lithography on two-dimensional nanomaterial (2D), i.e. multilayer MoS2, using AFM. The correlation of patterning behavior on the MoS2 flakes between the lithography conditions was investigated. The height and full width half maximum (FWHM) increase linearly with increasing tip voltage, even at different tip speeds, which is consistent with the results obtained from the Cabrera-Mott oxidation theory. The size of the clear relation decreases linearly with increasing tip speed, indicating that longer tip writing patterns result in more oxidation. The formation mechanism of the patterned oxide lines is presented along with LAO reaction processes.The final LAO lithography products have been demonstrated to be MoO2 and MoO3 by micro-Raman spectroscopy. These results show that LAO lithography using AFM is an effective technique for nanofabrication of nanodevices.

Формирование наноструктур из поликристаллических пленок диоксида ванадия с помощью сканирующей зондовой литографии

Vanadium dioxide (VO2) undergoes a reversible first-order metal-insulator phase transition near room temperature, accompanied by a structural phase transition. This causes a significant change in its electrical and optical properties, making it useful for practical applications. VO2-based nanostructures exhibit notable mechanical resistance to structural transition caused by their small size and demonstrate vivid properties during the phase transition. Obtaining VO2 nanostructures is an extremely demanded objective. This research study presents the use of scanning probe lithography techniques to fabricate nanostructures on polycrystalline VO2 films. The present study focuses on the modification of VO2 films when a positive bias is applied to the sample. The effect of the value and duration of the applied voltage, relative humidity on the quality of the formed nanolithographic pattern was analyzed. The oxidation mechanism was determined. It was found that as a result of local anodic oxidation the formed oxide structures consisting of vanadium penta-oxide (V2O5) completely dissolve in water. This process leads to the separation of the continuous polycrystalline VO2 film into individual nanostructures with precise dimensions. The presented method of forming nanostructures from crystalline VO2 films is promising for nanophotonics and nanoelectronics.

Local Anodic Oxidation of Silicon for Create Crossbar Architecture

Local Anodic Oxidation of Silicon for Create Crossbar Architecture

The Effect of Nanowire Gap for Silicon Nanowire Transistor to the Current-Voltage (I-Vds)

One-dimensional structures are attracting a lot of attention for optimizing applications as one of the most sensitive devices. Among the fabricated devices, silicon nanowires (SiNW) and silicon nanowire transistors (SiNWT) are of particular importance for promising applications fabricated using bottom-up or top-down approaches to nanoscale devices. In this paper, the sensitivity of the current-voltage characteristic to the nanowire gap of a silicon nanowire transistor (SiNWT) was analyzed. SiNWTs with different nanowire gaps were fabricated using scanning probe microscopy by local anodic oxidation (LOA). Varies gaps can be occurring during the fabrication processes and its can be controlled by RASTER programming in LAO. These gaps can give different results of the sensitivity to the volt-ampere response. However, these gaps can be neglected depending on the subject of the studies and important to the other study, especially in nano particle sensors. In this experiment, the nanowires gaps were developed in the range of 100.5-435.6 nm and had been plotted the measurement data with the volt-ampere response. The data was analyzed using a semiconductor analyzer connected to a HP 4156C SPA series software analysis model from Desert Cryogenics. From the results had been measured the Current-Voltage (IV) increases proportionally with the nanowire gap distance in the SINWT device and this results will give significant effects to the application in nanoparticle sensors

Direct etching of nano/microscale patterns with both few-layer graphene and high-depth graphite structures by the raster STM electric lithography in the ambient conditions.

The development of raster STM electric lithography has enabled the etching of nano/microscale patterns on both few-layer graphene (FLG) and high-depth graphite structures on the bulk HOPG substrates under ambient conditions. This approach utilises a nanoscale probe tip as a machining tool to directly fabricate conductive sample surfaces without the need for resists or masks. Compared to conventional nano/micro machining methods, the capability of ultraaccurate fabrication of nanoscale patterns using this technique is unmatched. The resulting FLG structures exhibit ultrasmooth flat bottoms and uniformly controlled depths ranging from 0.34 to 3.0nm (less than 10 layers). This work represents a significant advancement as it demonstrates the perfect etching of FLG structures in designated nano/microscale regions using raster STM electric lithography in the constant current mode, which reaches the limitation of top-down manufacturing techniques. Additionally, raster STM electric lithography in the constant height mode can directly etch high-depth structures (up to ∼100nm). The geometric shape and number of layers of the etched graphene structures determined by either local anodic oxidation (LAO) or the electric discharge (ED) mechanism. The LAO mechanism results in less debris and smoother edges compared to the ED mechanism, which is caused by the random electrical discharge between the tip and the sample. The well-controlled raster STM electric lithography technique is believed to be a promising and facile approach for constructing nano/microscale graphene-based devices.

SiC Doping Impact during Conducting AFM under Ambient Atmosphere.

The characterization of silicon carbide (SiC) by specific electrical atomic force microscopy (AFM) modes is highly appreciated for revealing its structure and properties at a nanoscale. However, during the conductive AFM (C-AFM) measurements, the strong electric field that builds up around and below the AFM conductive tip in ambient atmosphere may lead to a direct anodic oxidation of the SiC surface due to the formation of a water nanomeniscus. In this paper, the underlying effects of the anodization are experimentally investigated for SiC multilayers with different doping levels by studying gradual SiC epitaxial-doped layers with nitrogen (N) from 5 × 1017 to 1019 at/cm3. The presence of the water nanomeniscus is probed by the AFM and analyzed with the force-distance curve when a negative bias is applied to the AFM tip. From the water meniscus breakup distance measured without and with polarization, the water meniscus volume is increased by a factor of three under polarization. AFM experimental results are supported by electrostatic modeling to study oxide growth. By taking into account the presence of the water nanomeniscus, the surface oxide layer and the SiC doping level, a 2D-axisymmetric finite element model is developed to calculate the electric field distribution nearby the tip contact and the current distributions at the nanocontact. The results demonstrate that the anodization occurred for the conductive regime in which the current depends strongly to the doping; its threshold value is 7 × 1018 at/cm3 for anodization. Finally, the characterization of a classical planar SiC-MOSFET by C-AFM is examined. Results reveal the local oxidation mechanism of the SiC material at the surface of the MOSFET structure. AFM topographies after successive C-AFM measurements show that the local oxide created by anodization is located on both sides of the MOS channel; these areas are the locations of the highly n-type-doped zones. A selective wet chemical etching confirms that the oxide induced by local anodic oxidation is a SiOCH layer.

Atomistic insights into bias-induced oxidation on passivated silicon surface through ReaxFF MD simulation

The study investigated the bias-induced oxidation through ReaxFF molecular dynamics simulations in order to bridge the knowledge gaps in the understanding of physical–chemical reaction at the atomic scale. Such an understanding is critical to realise accurate process control of bias-induced local anodic oxidation nanolithography. In this work, we simulated bias-induced oxidation by applying electric fields to passivated silicon surfaces and performed a detailed analysis of the simulation results to identify the primary chemical components involved in the reaction and their respective roles. In contrast to surface passivation, bias-induced oxidation led mainly to the creation of Si–O–Si bonds in the oxide film, along with the consumption of H2O and the generation of H3O+ in the water layer, whereas the chemical composition on the oxidised surface remained essentially unchanged with a mixture of Si–O–H, Si–H, Si–H2, H2O–Si and Si–O–Si bonds. Furthermore, parametric studies indicated that increased electric field strength and humidity did not significantly alter the surface chemical composition but notably enhanced the bias-induced oxidation, as indicated by the increased number of Si–O–Si bonds and oxide thickness in simulation results. A good agreement is achieved between the simulation and experimental results.

Flexible single-step fabrication of programmable 3D nanostructures by pulse-modulated local anodic oxidation

A flexible single-step nanofabrication approach was developed using programmable pulse modulation local anodic oxidation for the efficient generation of various 3D nanostructures. The dependence of oxidation growth on pulse parameters was derived from parametric studies, from which an analytical process model was developed for the first time to link the pulse parameters with the geometry of 3D nanostructure with precision. The nanofabrication approach was implemented on an atomic force microscope. Experimental results show that this approach can effectively create 3D nanostructures with minimum feature sizes of sub-10 nm (lateral) and sub-nm (vertical) with nm and sub-nm level precision, respectively.

Forming‐Free Resistive Switching of Electrochemical Titanium Oxide Localized Nanostructures: Anodization, Chemical Composition, Nanoscale Size Effects, and Memristive Storage

AbstractElectrochemical anodization is a powerful method for the preparation of oxide thin films with controlled thickness, structure, and composition and proves as a promising approach to be applied to memristive devices. Here, experimental studies on titanium oxide nanoscale structures produced by local anodic oxidation and the influence of the thickness on the memristive properties are presented. Controllable preparation of forming‐free memristive cells with switching voltages less than 3 V are demonstrated. The chemical composition and oxidation state of the elements in the TiOxnanostructures are analyzed by means of X‐ray photoelectron spectroscopy, which reveals the formation of TiO2(458.4 eV), Ti2O3(456.6 eV), and TiO (454.8 eV). The increasing thickness of the devices from 4.5 ± 0.7 to 7.9 ± 0.3 nm leads to a decrease in the OFF to ON resistance ratio from 250 to 10.7, respectively. The mechanism of formation and resistive switching in the anodic devices is also discussed. The results can be applied to the design and development of technological processes for memristive structure manufacturing based on electrochemical oxidation.

Near-field infrared spectroscopy of SiOx nanowires

Scanning-probe-based patterning methods including local anodic oxidation have been widely used in nanotechnology to form various nanoelectronic device structures. However, so far spectroscopic investigations e.g. to determine the stoichiometry of oxide nanostructures with characteristic sizes below the diffraction limit do not exist. Using near-field infrared spectroscopy, we study the vibrational optical modes in SiOx nanowires with a height (width) of 2.1 nm (350 nm). The nanowires were produced by oxidation employing an atomic force microscope (AFM) on wide Si (111) terraces. The analysis of the spectroscopic data allows us to determine the composition of SiOx with a spatial resolution far below the diffraction limit. The composition × across SiOx nanowires is found to decrease from 1.6 in the center of the nanowire to 1.4 at its edges.

Local anodic oxidation of silicon for create crossbar architecture

Paper present possibility of creation a neuromatrix in the form crossbar architecture on a silicon substrate is shown. Crossbar architecture in the form of a set of nanosized conductors, between which there is a layer of titanium oxide, capable of changing its conductivity under the action of the applied voltage, it is proposed to form using the method of local anodic oxidation. The results is present of the study technological parameters of the method of local anodic oxidation silicon and titanium for the implementation of the elements of this neuromatrix in the form of a memristor structures. Keywords: Silicon, titanium, local anodic oxidation, neuromatrix, crossbar.

Локальное анодное окисление кремния для создания кроссбар-архитектуры

Paper present possibility of creation a neuromatrix in the form crossbar architecture on a silicon substrate is shown. Crossbar architecture in the form of a set of nanosized conductors, between which there is a layer of titanium oxide, capable of changing its conductivity under the action of the applied voltage, it is proposed to form using the method of local anodic oxidation. The results is present of the study technological parameters of the method of local anodic oxidation silicon and titanium for the implementation of the elements of this neuromatrix in the form of a memristor structures.

Nanoscale wafer patterning using SPM induced local anodic oxidation in InP substrates

Atomic force microscopy (AFM) assisted local anodic oxidation (LAO) offers advantages over other semiconductor fabrication techniques as it is a low contamination method. We demonstrate the fabrication of deep and highly reproducible nanohole arrays on InP using LAO. Nanohole and nano-oxide mound radius and depth are controlled independently by altering AFM tip bias and humidity, with a maximum nanohole depth of 15.6 ± 1.2 nm being achieved. Additionally, the effect of tip write speed on oxide line formation is compared for n-type, p-type and semi-insulating substrates, which shows that n-type InP oxidizes at a slower rate that semi-insulated or p-type InP. Finally, we calculate the activation energy for LAO of semi-insulating InP to be 0.4 eV, suggesting the oxidation mechanism is similar to that which occurs during plasma oxidation.

Photoluminescence enhancement in multilayered MoSe2 nanostructures obtained by local anodic oxidation

Monolayers of transition metal dichalcogenides (TMDCs) exhibit attractive properties and are promising for fabricating photonic and optoelectronic devices, while bulk multilayered structures based on the same materials only recently has revealed many properties useful for nanophotonics. In this regard, the combination of monolayer and multilayer properties in one device (on a single flake) is an important and fruitful task that needs to be solved. In this work, we demonstrate the use of local anodic oxidation to improve the optical properties of multilayer MoSe2 flakes on a gold-covered substrate. Using this method, we fabricated nanostructures demonstrating extraordinarily enhanced photoluminescence (PL), with an intensity up to three orders of magnitude compared to that of the original structure. Low-frequency Raman spectroscopy showed that the nature of this PL enhancement is that the bindings between the layers inside the nanostructures are severely disrupted. This means that the nanostructures consist of quasi-monolayers, which is in good agreement with the intensity and the position of PL peak. Here, we also propose a mechanism of forming these quasi-monolayers. Therefore, this method allows using multilayer TMDC flakes on a conductive substrate to fabricate areas with quasi-monolayer optical properties, exhibiting an enhanced PL intensity.

Study on the Physical Properties of a SiNW Biosensor to the Sensitivity of DNA Detection.

SiNW (silicon nanowire) arrays consisting of 5- and 10-wires were fabricated by using an atomic force microscope—the local anodic oxidation (AFM-LAO) technique followed by wet chemical etching. Tetramethylammonium hydroxide (TMAH) and isopropyl alcohol (IPA) at various concentrations were used to etch SiNWs. The SiNWs produced were differed in dimension and surface roughness. The SiNWs were functionalized and used for the detection of deoxyribonucleic acid (DNA) dengue (DEN-1). SiNW-based biosensors show sensitive detection of dengue DNA due to certain factors. The physical properties of SiNWs, such as the number of wires, the dimensions of wires, and surface roughness, were found to influence the sensitivity of the biosensor device. The SiNW biosensor device with 10 wires, a larger surface-to-volume ratio, and a rough surface is the most sensitive device, with a 1.93 fM limit of detection (LOD).

Advances in strain engineering on oxide heteroepitaxy

Advances in strain engineering on oxide heteroepitaxy

Nucleic Acid Sequence Detection by a Multi-Technique Approach

The development of highly sensitive, specific, cheap and rapid laboratory diagnostics is an increasingly important challenge. Diagnosis of virus or various cancer diseases can be achieved through nucleic acid sequence detection, able to recognize specific short DNA or RNA sequences. DNA-based biosensors are excellent candidates, thanks also to their reusable property. A careful multi-technique characterization of DNA self-assembled monolayers (SAMs) represents a crucial step in order to optimize a sturdy sequence detection scheme based on helix-helix hybridization. In our work, we exploit molecular self-assembly on gold of single 22/28-bases DNA strands complementary to specific disease-related RNA or DNA sequences. The characterization is based on microscopic (Atomic Force Microscopy, AFM), spectroscopic (Spectroscopic Ellipsometry, SE, and X-rays Photoelectron Spectroscopy, XPS) and mass-sensitive (Quartz-Crystal Microbalance with Dissipation, QCM-D) methods, in order to investigate structural, optical and packing properties of DNA films. By AFM nanolithography, regularly defined micro-areas were depleted from molecules under a high tip load: the depth of the shaved area provides an accurate estimate of the film thickness. Specific sequence recognition has therefore been detected by monitoring changes in the film thickness upon hybridization. Through SE experiments it has been possible to monitor the optical thickness (influenced by both thickness and refractive index) and the fingerprints of the 260 nm DNA molecular absorption, allowing to evaluate the hybridization state of a DNA monolayer through a non-destructive and rapid method. Finally, XPS measurements provided useful information about surface coverage, allowing to distinguish between single strand and double strand DNA monolayers, while by QCM-D we could follow the dynamic process and, from the changes in mass/area ratio, evaluate the molecular density.

Study of local anodic oxidation regimes in MoSe2

Scanning probe microscopy is widely known not only as a well-established research method but also as a set of techniques enabling precise surface modification. One such technique is local anodic oxidation (LAO). In this study, we investigate the LAO of MoSe2 transferred on an Au/Si substrate, focusing specifically on the dependence of the height and diameter of oxidized dots on the applied voltage and time of exposure at various humidities. Depending on the humidity, two different oxidation regimes were identified. The first, at a relative humidity (RH) of 60%–65%, leads to in-plane isotropic oxidation. For this regime, we analyze the dependence of the size of oxidized dots on the oxidation parameters and modify the classical equation of oxidation kinetics to account for the properties of MoSe2 and its oxide. In this regime, patterns with a maximum spatial resolution of 10 nm were formed on the MoSe2 surface. The second is the in-plane anisotropic oxidation regime that arises at a RH of 40%–50%. In this regime, oxidation leads to the formation of triangles oxidized inside the zigzag edges. Based on the mutual orientation of zigzag and armchair directions in successive oxidized layers, the stacking type and phase of MoSe2 flakes were determined. These results allow LAO to be considered not only as an ultra-high-resolution nanolithography method, but also as a method for investigating the crystal structure of materials with strong intrinsic anisotropy, such as transition metal dichalcogenides.

Anisotropy of local anodic oxidation process in thin MoSe2 films

In this work, various regimes of local anodic oxidation (LAO) of MoSe2 were studied. Here we show that there is a certain set of oxidation parameters that results in the anisotropic oxidation of MoSe2. In this mode, LAO leads to the formation of oxidized triangles. The triangles have the same orientation on the surface of the flakes, which indicates that MoSe2 is oxidized mainly along the crystallographic directions of the zigzag edges. These results can be useful for determining crystallographic directions of zigzag/armchair edges and the degree of single-crystallinity of MoSe2 flakes.