SiO2 Si Substrate Research Articles

Frequency and Polarization Response of Multipolar Gold Nanoantennae

Multipolarized nanoantennae are promising for terahertz applications due to their ability to support multiple resonance and polarization sensitivity. This study investigates the behavior of multipolarized gold nanoantennae placed on a Si-SiO2 substrate and compares their performance with antennae in air. The results show that the resonance frequency shifts from 27 THz in the air to 26 THz on the SiSiO2 substrate. SEM and FTIR analysis confirmed the antenna dimensions and optical response, with experimental reflectance spectra revealing resonance at 21 THz and 26 THz. The multi-polarized antenna demonstrated stable performance across different polarization angles compared to traditional dipole antennae, making it suitable for various terahertz applications. These findings provide insights into optimizing nanoantenna design for advanced sensors and communication systems.

Orientation dependent thermal behavior of CVD grown few layer MoS2 films

Differently oriented supported MoS2 nanostructures are ideal candidates for various electronic and optoelectronic applications, with their performance influenced by thermal properties and is still not comprehensively studied. In this paper, we study the temperature-dependent Raman response of CVD synthesized horizontally (H-MoS2) and vertically (V-MoS2) oriented MoS2 grown over SiO2-Si substrate from 80 to 333 K. The V-MoS2 shows a relatively higher peak shift, attributed to its smaller contact area with the substrate, giving it a suspended-like characteristic. Then to facilitate quantitative understanding of the non-linear temperature dependency in differently oriented MoS2 films, a physical model incorporating both volume and thermal effect is employed. The greater four-phonon contribution for in-plane mode of H-MoS2 compared to V-MoS2 may be attributed to the larger contact area with the substrate, leading to higher-order scattering due to interface formation. Our study can be leveraged for understanding thermal response in future applications of low-power thermoelectric and optoelectronic devices.

Flattened chains dominate the adsorption dynamics of loosely adsorbed chains on modified planar substrates.

Herein, the adsorption of polystyrene (PS) on phenyl-modified SiO2-Si substrates was investigated. Different from those for PS adsorption on a neat SiO2-Si substrate, the growth rate (vads) in the linear regime and hads/Rg (hads, thickness of flattened and loosely adsorbed layers on the substrate; Rg, radius of gyration) declined with increasing molecular weight (Mw) of PS and the phenyl content on the modified substrates, while the thickness of the flattened layer (hflat) and its coverage increased with increasing phenyl content. The results indicated that the adsorption of loose chains was controlled by the adsorption of flattened chains, as it only occurred in the empty contact sites remaining after the adsorption of flattened chains. Before approaching quasi-equilibrium (t < tcross), the number of flattened chain contact sites increased due to an enthalpically favorable process and, correspondingly, their spatial positions dynamically changed, which perturbed the adsorption of loose chains. When the adsorption of flattened chains reached quasi-equilibrium (t > tcross), the adsorption of loose chains was determined by the empty contact sites. The coverage of flattened chains and time to reach quasi-equilibrium were increased with more phenyl groups on the substrate, enhancing π-π interfacial interactions and resulting in a decreased adsorption rate and fewer loosely adsorbed chains. Mw-dependent vads and hads/Rg differed on phenyl-modified substrates compared to the neat SiO2-Si substrate owing to fewer empty contact sites for loose chains. The study findings improve our understanding of the mechanism responsible for the formation and structure of the adsorbed layer on solid surfaces.

Exploring Al2O3 blister evolution through cathodoluminescence and attenuated total reflectance infrared analyses

This work focuses on the morphological and optical evolution of Al2O3 thick films grown by atomic layer deposition on Si-SiO2 substrates. Blister formation has been the subject of extensive research in the literature; our work fills a crucial gap in the optical characterization of areas inside and outside blisters. Morphological studies were carried out by scanning electron microscopy; we found a reciprocal relationship between the density of the blisters and their diameter. The thickness and refractive index were studied by ellipsometry, revealing a systematic increase in the refractive index with increasing annealing temperature. In addition, we observed the hydrophobic behavior in all films using the water contact angle technique, which suggests that even with blisters, this material can be used in waterproof coatings. Using Auger spectroscopy, we confirmed that delamination occurs completely once the blisters are broken. In this work, we perform cathodoluminescence measurements outside and inside the ampoules. In the area outside the blisters, we observe emissions attributed to the F centers, and the change from the main peaks of 2.8 and 3.4 eV for the as-deposited film to the dominance of emissions centered at 3.4 and 3.7 eV is clearly observed. Furthermore, we observed a strong increase in the cathodoluminescence signal at higher annealing temperatures. On the other hand, we also observed the evolution of the blisters through the cathodoluminescence spectra; in that area, we observed the radical change in the spectrum once the blister is broken, giving rise to the SiO2 signals. We also observed this rupture through a new absorption band in the attenuated total reflectance IR spectra.

Highly Conducting Sc and Y co-doped Zirconia Solid Electrolyte Thin Films Prepared via Pulsed Laser Deposition for Solid Oxide Electrochemical Cells Applications

Scandium (Sc) and yttrium (Y) co-doped ZrO2 thin films were fabricated via pulsed laser deposition (PLD). The target material, 4 mol% Sc2O3 and 4 mol% Y2O3 co-doped ZrO2 (ScYSZ), was first synthesized via a solid-state reaction. The ScYSZ thin film was deposited on SiO2-Si substrate by laser ablation, using a Q-switched Nd3+:YAG laser (λ = 266 nm) and substrate temperatures of 600 and 800 oC. Micro-structural and conductivity properties of the resulting as-deposited thin films were investigated. X-ray diffraction (XRD) sample patterns revealed that the as-deposited polycrystalline films can be indexed to a cubic structure. In addition, varying the oxygen partial pressures during the deposition was studied. FE-SEM images revealed dense and crack-free surface morphologies achieved at lower oxygen partial pressures (0.01 Pa and 0.1 Pa) and rough surface with porous morphology at high oxygen partial pressures (1.0 Pa and 10 Pa). The thickness of the film is about 120 nm for the thin film deposited at 800 oC substrate temperature (TS). The total conductivity of the thin film was measured using electrochemical impedance spectroscopy (EIS). Interestingly, the calculated total conductivity of the deposited ScYSZ thin film, 0.1 Pa and TS at 800 oC, revealed about 2.8x10-1 S/cmat 700 oC and with activation energy (Ea) of 0.78 eV from 500 oC to 700 oC. The fabricated as-deposited ScYSZ thin film is one of the highest reported highly conducting solid electrolytes that is a promising material for fuel cell or electrolysis cell applications.

Optical Constants and Optical Anisotropy of Ultrathin Gold Films

Continuous and homogeneous thin gold films are fabricated on Si–SiO2 substrates using an additional seed layer based on Cu oxide or oxidized Cu. The optical properties of these gold films with thicknesses from 3 to 50 nm are studied with the help of variable angle spectroscopic ellipsometry. The optical constants and the dielectric functions of thin Au films in the wavelength range of 240–1700 nm are extracted by fitting measured ellipsometric data using the Fresnel isotropic and anisotropic models. By applying the Drude approximation to the infrared range, values of the plasma frequency ωp and relaxation time τ are obtained as a function of film thickness. It is found that plasma frequency ωp of the gold films is mostly constant in the thickness range of 3–50 nm with an average being close to the bulk value ωp ≈ 8.45 eV. The relaxation time decreases dramatically from the bulk values of τ ≈ 14 fs to τ ≈ 2 fs for gold films of 3 nm in an agreement with the confinement effect. It is established that the thinnest gold films (≈3 nm) are described better by an anisotropic layer and the underlying reasons for such optical anisotropy are discussed.

Development of hard x-ray photoelectron spectroscopy using synchrotron radiation x-ray up to 30 keV.

Hard X-ray photoelectron spectroscopy (HAXPES) is a powerful tool for investigating the chemical and electronic states of bulk and buried interfaces non-destructively due to its large probing depth. To obtain a much larger probing depth and measure deeper regions than conventional HAXPES, we have developed a high-energy HAXPES (HE-HAXPES) system excited by photon energies up to 30keV. This system is achieved by combining an applied bias voltage on the sample with a conventional hemispherical electron energy analyzer. By utilizing this system, we successfully observed a Si 1s peak from the bulk-Si substrate underneath the 110-nm-thick SiO2 film at a photon energy of 30keV. Moreover, the system found that the asymmetrical spectral shape of the Si substrate signal originated from the electronic state, which is upward band bending formed at the interface between the SiO2 film and Si substrate. The HE-HAXPES system, excited by photon energy up to 30keV, could be a very useful tool to yield genuine insights into the chemical and electronic states in deeply buried regions.

XAS studies of vanadium pentoxide thin films

Thin films of 200 nm of VOx RF magnetron sputtered on the SiO2 glass and Si substrates were studied with X-ray Absorption Spectroscopy in the XANES range of the oxygen K and vanadium L2,3 edges. The total electron yield (TEY) detection mode was used. The spectra were collected at several temperatures between room temperature and 300 °C for the unpolarized and linearly polarized beam to study polarization effects. The experimental data were compared with the theoretical model based on DFT-ROCIS (Density Functional Theory, Restricted Open shell Configuration Interaction with Singles) from the literature. Changes in the spectra with temperature, particularly visible at the oxygen K edge are attributed to the loss of surface oxygen and the corresponding changes of population of the single- double- and triple vanadium coordinated oxygen. The corresponding decrease of the surface stoichiometry leads to formation lower than V5+ valency of vanadium ions such as V4+ or V3+ i.e., containing d-electrons. It gives a tentative explanation for the occurrence of metallicity attributed in the literature to a metal–insulator transition (MIT).

Hybrid 2D–CMOS microchips for memristive applications

Exploiting the excellent electronic properties of two-dimensional (2D) materials to fabricate advanced electronic circuits is a major goal for the semiconductor industry1,2. However, most studies in this field have been limited to the fabrication and characterization of isolated large (more than 1 µm2) devices on unfunctional SiO2–Si substrates. Some studies have integrated monolayer graphene on silicon microchips as a large-area (more than 500 µm2) interconnection3 and as a channel of large transistors (roughly 16.5 µm2) (refs. 4,5), but in all cases the integration density was low, no computation was demonstrated and manipulating monolayer 2D materials was challenging because native pinholes and cracks during transfer increase variability and reduce yield. Here, we present the fabrication of high-integration-density 2D–CMOS hybrid microchips for memristive applications—CMOS stands for complementary metal–oxide–semiconductor. We transfer a sheet of multilayer hexagonal boron nitride onto the back-end-of-line interconnections of silicon microchips containing CMOS transistors of the 180 nm node, and finalize the circuits by patterning the top electrodes and interconnections. The CMOS transistors provide outstanding control over the currents across the hexagonal boron nitride memristors, which allows us to achieve endurances of roughly 5 million cycles in memristors as small as 0.053 µm2. We demonstrate in-memory computation by constructing logic gates, and measure spike-timing dependent plasticity signals that are suitable for the implementation of spiking neural networks. The high performance and the relatively-high technology readiness level achieved represent a notable advance towards the integration of 2D materials in microelectronic products and memristive applications.

Control of Columnar Grain Microstructure in CSD LaNiO3 Films.

Conductive LaNiO3 (LNO) films with an ABO3 perovskite structure deposited on silicon wafers are a promising material for various electronics applications. The creation of a well-defined columnar grain structure in CSD (Chemical Solution Deposition) LNO films is challenging to achieve on an amorphous substrate. Here, we report the formation of columnar grain structure in LNO films deposited on the Si-SiO2 substrate via layer-by-layer deposition with the control of soft-baking temperature and high temperature annealing time of each deposited layer. The columnar structure is controlled not by typical heterogeneous nucleation on the film/substrate interface, but by the crystallites' coalescence during the successive layers' deposition and annealing. The columnar structure of LNO film provides the low resistivity value ρ~700 µOhm·cm and is well suited to lead zirconate-titanate (PZT) film growth with perfect crystalline structure and ferroelectric performance. These results extend the understanding of columnar grain growth via CSD techniques and may enable the development of new materials and devices for distinct applications.

Structure of the Poly(methyl methacrylate) Adsorbed Layer Determined by the Surface Chemistry of the Substrate

The adsorbed polymer layer on the inorganic solid surface is crucial in improving the physical properties of composite nanomaterials; therefore, the properties could be tuned by altering the structure of the adsorbed layer. We investigated poly(methyl methacrylate) (PMMA) adsorbed layers on SiO2–Si substrates by varying the hydroxyl (OH) group content on the substrate surface. The results indicated that the thicknesses of the flattened layer and loosely adsorbed layer decreased with decreasing OH group content and the flattened layer disappeared when the content was ∼31%. The OH groups controlled the formation of the adsorbed layer, providing anchor points through hydrogen bonding with the carbonyl groups in PMMA. With decreasing OH group content, fewer anchor points possibly prevented train conformation and the relatively stable loosely adsorbed chains still formed, which enhanced the segmental dynamics of the ultrathin PMMA film. These results provide novel insight into the role of surface chemistry in forming adsorbed polymer layers on substrates.

RF and Crosstalk Characterization of Chip Interconnects Using Finite Element Method

This paper presents new finite element method (FEM) based approach for radio frequency (RF) and crosstalk (X talk) characterization of chip interconnects. Being based on scattering parameters (S-parameters), this approach truly and accurately demonstrates the transmission line behavior of chip interconnects over a wideband of frequencies. To demonstrate FEM based method, a single-line and a 3-line interconnect test structures on SiO2-Si substrate have been designed and simulated in High Frequency Structure Simulator (HFSS). The RF and crosstalk characterization of chip interconnect materials Copper (Cu), doped multilayer Graphene Nanoribbon (DMLGNR), and neutral multilayer Graphene Nanoribbon (NMLGNR) have been demonstrated in terms of transmission coefficient (Sij & Smn) from 1 to 1000 GHz. The single-line three-dimensional (3D) structures comprising of Cu, DMLGNR, and NMLGNR have maximum transmission loss values of -15.93 dB, -22.03 dB, and - 13.73 dB at frequencies of 643 GHz, 402 GHz, and 643 GHz, respectively whereas three-line bus structure exhibit maximum victim-line transmission loss values of -15.28 dB, -17.47 dB, and -15.98 dB at frequencies of 247 GHz, 829 GHz, and 377 GHz, respectively. Further, the crosstalk results have demonstrated that as frequency increases significant crosstalk is observed between nearby lines due to electromagnetic interference and coupling (EMI/EMC) issues.

Thermal Oxidation of Tungsten Coatings for Detection by Infrared Spectrometry Method

Physical vapor deposition (PVD) of metallic thin films is used extensively in the fabrication of semiconductor technology devices - use as of lately for them have grown. Tungsten (W) is a low resistivity, refractory metal, that is often deposited by PVD methods for use as a gate contact to semiconductor devices and due to the low work function and high thermal stability, W can be used for the fabrication of field emitters in microelectronics [1-3]. In order to monitor quality of the synthesized thin films by magnetron sputtering method, it is necessary to develop methodology suitable for the analysis of these thin films. Infrared spectrometry is a sensitive method for the analysis of chemical bonds, but W thin films contain weakly polar and non-polar W-W bonds, that cannot be directly detected by infrared spectrometry, therefore oxidation of W is selected as thermal oxidation method for detecting oxidized products for thin films of thickness 150 nm, for instance, W-O bonds. After oxidation, it was observed, that the oxidation of W thin films takes place already at a 600 °C in the air atmosphere. The Fourier transform infrared spectrometry (FTIR) spectra of modified coatings showed formation of additional new signals in the region of 700-900 cm−1 attributed to W-O, O-W-O, W=O bonds - formation of W-oxygen bonds on Si-SiO2 substrate was achieved. For coating homogeneity and production quality formation, additionally synthesized control samples are recommended for FTIR analysis.

Flexible control of multi-focus with geometric phase encoded metalens based on the complex digital addition principle

A transmissive encoding metasurface based on the geometric phase principle is proposed. The encoding unit adopts an anisotropic Si dielectric strip and SiO2 substrate on the upper layer, and realizes the phase modulation of the incident wave in the span of 0–2π on the premise of achieving high polarization conversion efficiency. 1-bit, 2-bit and even multi-bit coding units are constructed by rotating surface units. In order to realize the multi-focus function of imaging space, we propose to introduce the principle of complex code addition into the design of metalens. Compared with traditional scalar encoding, complex encoding reveals the intrinsic connection between different encoded bits, thus closer to the essence of electromagnetism. The multi-angle control of multi-focus in free space is realized by the complex coding of four groups of single-focal metalenses and their addition operations. The multifocal metalens at this time also has the angular characteristics of the previous single focus lens, and multiple angles have no influence on each other. Our proposed complex additive multifocal metalens provides a new idea for future multifocal metalens design, especially the design of polarization-sensitive devices.

FTIR Analysis of Oxidized Tungsten and Tungsten Diboride Nanolayers

Tungsten (W) and tungsten diboride (WB2) materials can be used to fabricate electron emission layers in field emission microelectronic devices. The characterization and quality assurance of synthesized films is crucial for the good performance of the devices. W and WB2 nanofilms with a thickness of 150 nm and 200 nm were deposited on the Si-SiO2 substrate by the magnetron sputtering technique. The synthesized layers were thermally treated in a thermal analysis device under various gas flow conditions (varying Ar; N2; synthetic air; air with O2, N2, and moisture (further in this text – laboratory air)) and after oxidation, FTIR (Fourier transform infrared spectrometry) spectra were registered. FTIR spectra of the as-deposited layers showed weak peaks related to Si-O and Si-O-Si bonds from the substrate and considered for the analysis of the layers. Several new peaks occur in the spectra of the thermally treated layers. Of the oxidation layers, new peaks related to nanolayers, were observed W-O bonds, it is noticeable that the spectra vary with each other with signal intensity and offsets. In each experimental environment with various gas flow conditions, there were W=O bonds observed, also in every environment except in laboratory air with the flow, B-O bond was detected for about 1300 – 1350 cm-1 range. It was shown that thermal oxidation of W and WB2 layers can be applied for the analysis of W and WB2 layers on SiO2 substrate by forming W and B oxides using treatment in high temperature and detection of their bonds by FTIR.

Humidity Sensor Based on rGO-SDS Composite Film.

Based on the humidity testing requirements in different environments, this paper investigates the humidity sensitivity of reduced graphene oxide (rGO)-sodium dodecyl sulfate (SDS) composite film humidity sensor. In the experiments, rGO-SDS dispersions with a concentration of 5 mg/mL were prepared, and a microelectromechanical system (MEMS) process was used to prepare the interdigital electrodes. The dispersions were then drop-coated on the interdigital electrodes and dried on a heated plate at 100 °C. The surface characteristics of the rGO-SDS films transferred onto SiO2-Si substrates were analyzed by scanning electron microscopy, raman spectroscopy and atomic force microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and tested by a correlation system, which showed a linear relationship between humidity variation and the resistance variation of the sensor in the ambient humidity range of 25–95% RH. At room temperature, the linearity of the sensor is about 0.98431 and the sensitivity is about 11.41432 Ω/% RH. At 100 °C, the correlation of the sensor is about 0.95046 and the sensitivity is about 1.0145 Ω/% RH; with a response time of only 9 s at ambient humidity from 25% RH to 95% RH, the sensor has very good repeatability and stability.

Detection of individual spin species via frequency-modulated charge pumping.

We utilize a frequency-modulated charge pumping methodology to measure quickly and conveniently single "charge per cycle" in highly scaled Si/SiO2 metal-oxide-semiconductor field effect transistors. This is indicative of detection and manipulation of a single interface trap spin species located at the boundary between the SiO2 gate dielectric and Si substrate (almost certainly a Pb type center). This demonstration in sub-micrometer devices in which Dennard scaling of the gate oxide has yielded extremely large gate oxide leakage currents eliminates interference between the charge pumping current and the leakage phenomenon. The result is the ability to measure single trap charge pumping reliably and easily, which would otherwise be completely inaccessible due to oxide leakage. This work provides a unique and readily available avenue for single spin species detection and manipulation, which can be applied as a quantized standard of electrical current as well as to serve as a potentially useful platform for developing quantum engineering technologies. Finally, we discuss potential underlying physical mechanisms that are involved in producing a seemingly contradictory measure of both odd and even integer values for charge per cycle.

Transport properties and crystallization of Li–Nb–O system on silicon

The present work is focused on the investigation of transport properties of LiNbO3 films synthesized through the crystallization of amorphous coatings as an alternative approach of high-quality films formation. Li–Nb–O amorphous films were deposited onto SiO2–Si substrates by the radio-frequency magnetron sputtering (RFMS) technique in an Ar environment. As-grown films crystallize under thermal annealing (TA) at the temperature of up to 600 °C with a formation of LiNbO3. The Hall effect analysis revealed that electrons are the major carriers in as-grown amorphous films, with the small-polaron hopping as a prime charge transport mechanism. TA in air provokes the increase in the carrier concentration from 6·1011 cm-3 to 6·1014 cm-3, originated from the NbLi antisite defect generation due to Li2O loss. We detected two concurrent transport processes contributing the net Hall mobility: the grain boundary limited and the bulk single-crystal limited mobility. Our results suggest that during the crystallization process, grain boundaries start playing a dominant role in charge transport, whereas when the grains get larger under recrystallization, the bulk single-crystal mobility prevails. The activation energy of the Hall mobility (Eaμ) and conductivity (Eaσ) has been determined for the studied films after TA at various temperatures. Eaμ rises non-monotonically from 0.1 eV with the annealing temperature and reaches a peak of 0.61 eV at a temperature of about 550 °C, which correlates with the trap concentration in LN films after TA. Besides, as followed from our analysis, the Nb4+ defects (electronic traps) are generated at the grain boundaries under TA and after recrystallization the intergranular barriers with the height of 0.5 eV limit the charge transport processes.

Effects of Oxygen Partial Pressure and Substrate Temperature on the Structure and Morphology of Sc and Y Co-Doped ZrO2 Solid Electrolyte Thin Films Prepared via Pulsed Laser Deposition.

Scandium (Sc) and yttrium (Y) co-doped ZrO2 (ScYSZ) thin films were prepared on a SiO2-Si substrate via pulsed laser deposition (PLD) method. In order to obtain good quality thin films with the desired microstructure, various oxygen partial pressures ( from 0.01 Pa to 10 Pa and substrate temperatures (Ts) from 25 °C to 800 °C were investigated. X-ray diffraction (XRD) patterns results showed that amorphous ScYSZ thin films were formed at room substrate temperature while cubic polycrystalline thin films were obtained at higher substrate temperatures (Ts = 200 °C, 400 °C, 600 °C, 800 °C). Raman spectra revealed a distinct Raman shift at around 600 cm−1 supporting a cubic phase. However, a transition from cubic to tetragonal phase can be observed with increasing oxygen partial pressure. Photoemission spectroscopy (PES) spectra suggested supporting analysis that more oxygen vacancies in the lattice can be observed for samples deposited at lower oxygen partial pressures resulting in a cubic structure with higher dopant cation binding energies as compared to the tetragonal structure observed at higher oxygen partial pressure. On the other hand, dense morphologies can be obtained at lower (0.01 Pa and 0.1 Pa) while more porous morphologies can be obtained at higher (1.0 Pa and 10 Pa).

Effect of ionizing irradiation on charge distribution and breakdown of MOSFETs

The effect of ionizing radiation on the formation of charges at internal SiO2-Si (substrate) and external SiO2-Sips (gate) interfacial boundaries (IFB) and on the gate breakdown of MOSFETs is studied. It is shown that with an increase in the dose of ionizing radiation near the internal interfacial boundaries, a monotonous increase of positive charge in p-MOSFETs, and the accumulation of positive charges at first, and at doses above 105 rad the accumulation of negative charges in n-MOSFETs is observed. Near the external interfacial boundaries, at low radiation doses, positive charge accumulation is observed, and at doses &gt;106 rad, negative charge in both p- and n-MOSFETs is observed. Up to a dose of 108 rad ionizing radiation dies not have a noticeable effect on the gate breakdown voltage in both p- and n-MOSFETs at both bias polarities. The absence of influence is explained by a breakdown by mechanism of anode hole injection. Keywords: ionizing radiation, MOSFETs, charge accumulation, gate breakdown.