Variable Angle Spectroscopic Ellipsometry Research Articles

Accurate band alignment of sputtered Sc2O3 on GaN for high electron mobility transistor applications

Abstract Sc2O3 is a promising gate dielectric for surface passivation in GaN-based devices. However, the interface quality and band alignment of sputtered Sc2O3 on GaN is not fully explored. In this work, X-ray photoelectron spectroscopy (XPS) and variable angle spectroscopic ellipsometry (VASE) wereperformed to extract the discontinuities in the valence and conduction band of Sc2O3/GaN system. Sc2O3 films were deposited on GaN using radio frequency sputtering. The valence band offset of Sc2O3/GaN was deterimened to be 0.76±0.1 eV using Kraut's method. The Sc2O3band gap of 6.03± 0.25 eV has been measured using O 1s energy loss spectroscopy. The electron affinity measurements of GaN and Sc2O3 using XPS secondary electron cut-off spectra provide additional degree of accuracy to derived band line-up for Sc2O3/GaN interface. The band alignment results are compared with literature values of bandoffsets determined experimentally and theoretically for differently grown Sc2O3films on GaN.

Congenital Zika virus infection impacts on male mouse offspring's reproductive biology.

Congenital ZIKV infection promotes alarming effects on male offspring's reproductive biology. This study showed the presence of the ZIKV antigen in the testis parenchyma, decreased testosterone levels, and sperm abnormalities in male offspring born to infected mothers. Infection with ZIKV during pregnancy is associated with fetal developmental problems. Although neurological issues are being explored more in experimental studies, limited research has focused on the reproductive health consequences for offspring born to infected mothers. In this context, this study aimed to assess the impact of ZIKV infection during pregnancy on the testes and sperm of adult male offspring. Female mice were intraperitoneally inoculated with a Brazil strain of ZIKV during the 5.5th day of embryonic gestation. The offspring were evaluated 12 weeks after birth to analyze cellular and molecular changes in the testes and sperm. A novel approach combining variable-angle spectroscopic ellipsometry and machine learning modeling was also introduced for sperm sample analysis. The study revealed the presence of ZIKV protein in the testis parenchyma of adult male offspring born to infected mothers. It was shown that the testes exhibited altered steroidogenesis and inflammatory mediators, in addition to significant issues with spermiogenesis that resulted in sperm with DNA fragmentation, head defects, and protamination failure. Additionally, sperm dielectric properties and artificial intelligence showed potential for rapid identification and classification of sperm samples from infected mice. These findings provide crucial insights into the reproductive risks for men born from ZIKV-infected pregnant women.

Disentangling Thermal from Electronic Contributions in the Spectral Response of Photoexcited Perovskite Materials.

Disentangling electronic and thermal effects in photoexcited perovskite materials is crucial for photovoltaic and optoelectronic applications but remains a challenge due to their intertwined nature in both the time and energy domains. In this study, we employed temperature-dependent variable-angle spectroscopic ellipsometry, density functional theory calculations, and broadband transient absorption spectroscopy spanning the visible to mid-to-deep-ultraviolet (UV) ranges on MAPbBr3 thin films. The use of deep-UV detection opens a new spectral window that enables the exploration of high-energy excitations at various symmetry points within the Brillouin zone, facilitating an understanding of the ultrafast responses of the UV bands and the underlying mechanisms governing them. Our investigation reveals that the photoinduced spectral features remarkably resemble those generated by pure lattice heating, and we disentangle the relative thermal and electronic contributions and their evolutions at different delay times using combinations of decay-associated spectra and temperature-induced differential absorption. The results demonstrate that the photoinduced transients possess a significant thermal origin and cannot be attributed solely to electronic effects. Following photoexcitation, as carriers (electrons and holes) transfer their energy to the lattice, the thermal contribution increases from ∼15% at 1 ps to ∼55% at 500 ps and subsequently decreases to ∼35-50% at 1 ns. These findings elucidate the intricate energy exchange between charge carriers and the lattice in photoexcited perovskite materials and provide insights into the limited utilization efficiency of photogenerated charge carriers.

Variable Angle Spectroscopic Ellipsometry Characterization of DMOAP-Functionalized Graphene Oxide Films

In our research, we investigated the optical properties of Graphene Oxide (GO) films functionalized with N,N-Dimethyl-N-octadecyl(3-aminopropyl)trimethoxysilyl chloride (DMOAP) using Variable Angle Spectroscopic Ellipsometry (VASE). We found that after the functionalization process, there was a notable increase in the thickness of the GO films. Additionally, there were observable changes in the Lorentz oscillator parameters, signaling modifications in the electronic transitions and structural properties of the films. Our results indicate that the functionalization with DMOAP not only impacts the electronic conjugation within the GO structures but also enhances the optical conductivity of the films, which is a finding of significant importance for potential applications in electronics, photonics, and materials science.

Dual-functional poly(2-methyl-2-oxazoline)/poly(2-(dimethylamine)ethyl methacrylate) mixed brushes with switchable protein adsorption and antibacterial properties

Herein, binary mixed brushes consisting of poly(2-methyl-2-oxazoline) (PMOXA) and poly(2-(dimethylamine)ethyl methacrylate) (PDMAEMA) with different chain lengths were fabricated by successive grafting of NH2-terminated PMOXA and SH-terminated PDMAEMA onto polydopamine-anchored substrates. The mixed-brush coating was characterized by variable-angle spectroscopic ellipsometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, zeta potential measurements, water contact angle, and atomic force microscopy. The mixed brushes showed tunable surface charge, wettability, and surface roughness, depending on the degree of PDMAEMA swelling under varying pH and ionic strength (I). Then the adsorption behaviors of pepsin, bovine serum albumin (BSA), γ-globulin, and lysozyme, four very different proteins with regard to isoelectric point, on the mixed brushes coating were studied by using fluorescence microscopy and surface plasmon resonance. When the chain length of PDMAEMA was about twice as long as PMOXA, the mixed brushes not only had high adsorption capacity for pepsin, BSA, and γ-globulin but also had a desorption efficiency of 86.9%, 87.1%, and 93.5%, respectively. It is explained that electrostatic attraction between the protonated PDMAEMA and positively charged acidic proteins (pepsin and BSA, whose isoelectric points were below the pKa of PDMAEMA) would drive the intensive adsorption (at pH 3, I = 10−3 mol·L−1 for pepsin, and pH 5, I = 10−5 mol·L−1 for BSA), while desorption was dominated by the hydrophilic PMOXA when PDMAEMA was shrinking (at pH 7, I = 10−1 mol·L−1 for pepsin, and pH 9, I = 10−1 mol·L−1 for BSA). Furthermore, the isoelectric precipitation led to the adsorption of neutral protein (γ-globulin, whose isoelectric point was near the pKa of PDMAEMA) at pH 7, I = 10−5 mol·L−1, while electrostatic repulsion and antifouling PMOXA triggered the desorption of γ-globulin at pH 3, I = 10−1 mol·L−1. However, alkaline protein (lysozyme, whose isoelectric point was higher than the pKa of PDMAEMA) exhibited slight adsorption on PMOXA/PDMAEMA mixed brushes under test conditions, regardless of whether PMOXA or PDMAEMA occupied the outermost layer. The antibacterial property of the mixed brushes against Escherichia coli was investigated. PMOXA/PDMAEMA mixed brushes showed significant bactericidal activity at pH 3, I = 10−3 mol·L−1, while the rinse of pH 9, I = 10−1 mol·L−1 solution could remove most of the residual bacteria. This work not only enables controlled adsorption of proteins with different isoelectric points but also ensures that the surface of the coating is minimized from bacterial contamination.

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.

Evolution of the characterization of horizontally aligned organic light‐emitting molecules and their recent progress of molecular design

AbstractThis review article surveys the organic small molecular materials, light‐emitting for most of them, being studied for the molecular alignment or orientation in thin films. Following a chronicle order, three practical characterization techniques, variable angle spectroscopic ellipsometry (VASE), angle‐dependent photoluminescence (ADPL), and grazing incidence wide‐angle x‐ray scattering (GIWAXS) have been used to probe phosphorescence, thermally activated delayed fluorescence (TADF) materials, as well as those of non‐phosphorescence and non‐TADF materials.

Optical and Structural Properties of Europium-Doped Silicon Oxide Fabricated Using Integrated Sputtering and Chemical Vapour Deposition

Europium (Eu) doped silicon oxide (SiOx) thin films containing Eu concentrations of 0.2 to 6.4 at% were fabricated using a hybrid deposition system combining a magnetron sputtering gun serving as the doping source with electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD). The influence of annealing conditions on the structural and luminescence properties was thoroughly studied. The optical properties of the films were investigated by performing variable angle spectroscopic ellipsometry (VASE) and photoluminescence (PL) measurements. The Eu-related emission was found to be highly dependent on the deposition parameters and annealing conditions. Eu2+ and Eu3+ emissions, which are attributed to blue and red light emissions, respectively, were observed. The structural properties were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses, and the formation of nanoclusters was confirmed. At annealing temperatures of 900 °C and beyond, EuxSiyOz crystals were formed, and Eu ions were optically activated. As the light emissions of these thin films are in the blue and red wavelength range, they are promising candidates to be used as greenhouse covers and transparent solar cells.

Indium-zinc-oxide thin films produced by low-cost chemical solution deposition: Tuning the microstructure, optical and electrical properties with the processing conditions

Indium-zinc-oxide (IZO) films were prepared by spin coating an ethanol-ethylene-glycol precursor solution with a Zn/(In + Zn) ratio of 0.36 on glass. The effects of temperature on the structure, microstructure, electrical, and optical properties of the IZO thin films were investigated by thermal analysis, Fourier-transform infrared spectroscopy, X-ray diffraction, electron and atomic-force microscopy, X-ray photoelectron spectroscopy and variable-angle spectroscopic ellipsometry. The prepared IZO thin films heated at 500, 600, and 700 °C in air were transparent, without long-range ordering, and with an RMS surface roughness of less than 1 nm. The lowest electrical resistivity at room temperature, 0.0069 Ωcm, was observed for the 115-nm-thick IZO thin film heated at 600 °C in air and subsequently post-annealed in Ar/H2. The thin film exhibited a microstructure characterized by grains typically 20 nm in size and had no organic residues. This film exhibits uniaxial optical anisotropy due to its ultra-thin lamellae with a high electron density. The ordinary refractive index was fitted as a Tauc-Lorentz-Urbach function, which is typical of an indirect absorption edge occurring in amorphous semiconductor materials. The principal absorption peak with an onset at about 2.8 eV and a Tauc gap energy of ∼2.6 eV is similar to those observed for In2O3. The described process of chemical solution deposition and subsequent curing is promising for the low-cost fabrication of IZO thin films for transparent electronics, and can be used to tune the structure and microstructure of IZO thin films, as well as their electrical and optical properties.

Optical Properties of Sputtered Iron Sulfide for Photonic Device Applications

Iron Pyrite is an earth-abundant, non-toxic, low-cost material commonly referred to as fool’s gold due to its golden-yellow appearance. It belongs to the family of transition metal dichalcogenides (TMDs) and gained fame as a potential solar material during the 70s and 80s. The reason was its suitable band gap and excellent absorption coefficient. However, the performance of pyrite never achieved a beneficial place among other materials and remained a mysterious path of research so far. With advanced technology and better characterization techniques and equipment available, the focus is again shifting towards exploring pyrite as a potential photovoltaic material which can compete with other materials, such as silicon, primarily in terms of cost. However, the true nature of pyrite and its application in photovoltaics cannot be adequately defined without looking deeply into its optical properties and interaction with light [1-3].Here in this work, we explored the photosensitivity of pyrite thin films at different thicknesses. These thin films were fabricated using an RF-powered sputtering method using a 99.9% FeS2 target. P-doped silicon and fused silica were used as substrates. The pressure and RF power were kept at 03 mTorrs and 70 watts, respectively, and the procedure took place at room temperature with an argon gas flow rate of ~24 cm3/min. The thickness was controlled by varying the sputtering time from 20 to 90 mins. As-prepared pyrite films were characterized through variable angle spectroscopic ellipsometry (VASE) and UV-vis spectrophotometer. An optical model was first developed for VASE in which the thin pyrite film showed light-absorbing characteristics (B-spline). Based on that model, the film thickness was determined. It was observed that the thickness of pyrite increased linearly with time, having grown to ~100 nm after 90 minutes of sputtering.UV-vis spectrophotometry was used to collect the transmission, reflectance and absorbance data for the films deposited onto a fused silica substrate. It was observed that the films showed very high absorbance in the UV range, and the absorbance tended to increase with the increase in thickness. The direct band gap was then calculated using absorbance data and building Tauc’s plot, which was observed to be around 2.25 eV.In conclusion, owing to its suitable properties and optical characteristics, iron pyrite opens many paths to scientists and researchers to explore its utilization not only in photovoltaics but also in other opto-electronic fields. However, further studies are also required to deeply understand its mechanism and capability. Nonetheless, high absorption of light in UV and visible range at very thin layers, suitable band gap and easy accessibility could be breakthrough parameters in near future for pyrite.

Electron affinity of metal oxide thin films of TiO2, ZnO, and NiO and their applicability in 28.3 THz rectenna devices

The holy grail of achieving efficient operation of infrared (IR) rectennas continues to be the realization of a high performance rectifier. In this paper, we have fabricated metal–insulator–metal (MIM) diodes based on TiO2, ZnO, and NiO thin films using shadow mask evaporation, photolithography, and sputtering. The electron affinities of oxides have been measured by a combination of variable angle spectroscopic ellipsometry and x-ray photoelectron spectroscopy, as well as deduction from the extraction of metal/oxide barrier heights of Fowler–Nordheim tunneling plots. Our results confirm a low value for the electron affinity of NiOx of ∼2.1–2.5 eV, which correlates with the high zero-bias dynamic resistance (RD0) of ∼500 kΩ of an associated MIM diode. These values render NiOx to be unsuitable for use in a rectenna device. Better performance has been observed from diodes based on TiO2 and ZnOx films. The best rectification performance was achieved for a Au/2.6 nm ZnOx/Cr diode, scaled down to 1 μm2 device area, showing a zero-bias dynamic resistance of RD0 = 71 kΩ, zero-bias responsivity β0 = 0.28 A/W, and a coupling efficiency of ηc = 2.4 × 10−5% for rectification at 28.3 THz. The main significance of this study is that it employs a methodology whereby key parameters of the MIM stack are derived from physical measurements, which are then used to assist in the fitting of electrical current–voltage data to produce a reliable appraisal of diode performance in an IR rectenna.

Mechanical and optical properties of amorphous silicon nitride-based films prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition

Silicon nitride (SiNx) based films have been recognized as essential dielectric films in the microelectronics and optoelectronics industry due to their desirable properties, such as high electrical insulation, excellent thermal stability, and compatibility with integrated circuit fabrication processes. They are also a potential candidate for fabricating wavelength-selective reflective coatings and surface passivation layers in building-integrated photovoltaics technologies. SiNx-based films are one of the popular choices for antireflective coatings in photovoltaics as well. Recently, SiNx and oxynitride (SiOyNx) based thin film optical filters have been explored to provide distinct color rendering to solar-charged electrical vehicles. Since solar cells have a lifespan of many years and the coating surfaces are substantial, it is essential to produce films with controlled optical and mechanical properties and maintain mechanical integrity against corrosion and wear. This study aims to design a deposition process and optimize minimal parameters for stable plasma conditions during multilayer deposition of SiNx and SiOyNx films using an electron cyclotron resonance plasma-enhanced chemical vapor deposition reactor with SiH4/N2/O2/Ar precursor mixtures at 120 °C. The primary goal was to investigate the influence of gas flow adjustments on the optical and mechanical properties, specifically targeting the refractive index and mechanical properties of the films. We measured the refractive index and the absorption of the films using variable angle spectroscopic ellipsometry. Then, we evaluated the mechanical residual stress ex situ using the wafer curvature measurement method. We have determined the elastic modulus and the hardness of the films using nanoindentation. The experimental results have shown a significant dependence of the optical and mechanical properties on the deposition parameters. To investigate the factors contributing to the intrinsic mechanical stress and to better understand SiNx film degradation mechanisms, we have studied the effect of postdeposition thermal cycling on the properties of the films. Several thermal-cycling experiments from room temperature to 400 °C were performed on different SiNx films, and the results showed an irreversible variation of the mechanical stress toward the tensile stresses caused by delamination of the films, while the refractive index remained unchanged.

Optical constants of polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As determined by variable-angle spectroscopic ellipsometry

The optical constants of single-crystal AlxGa1−xP and AlxGa1−xAs have been widely studied at various Al compositions but have not yet been thoroughly investigated as polycrystalline materials. Using variable-angle spectroscopic ellipsometry, we estimate and analyze the optical constants of polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As that were non-epitaxially deposited at deposition temperatures of either 250 or 420 °C, and with various dopant species, dopant concentrations, and V/III flux ratios. For wavelengths of 350–400 nm, decreasing the V/III ratio increases the refractive index of Be-doped polycrystalline Al0.25Ga0.75P. For wavelengths >500 nm, as the targeted Be dopant concentration increases for polycrystalline Al0.25Ga0.75P, the amount the extinction coefficient increases and the indirect bandgap decreases depends on the V/III ratio. Furthermore, Si-doped polycrystalline Al0.25Ga0.75P has significantly smaller extinction coefficient values than when it is Be-doped, for the same V/III ratio and targeted doping concentration, at wavelengths >500 nm. Based on our findings, we hypothesize that the dopant species, dopant concentration, and the V/III ratio dictate various types of defect concentrations, which then affect the optical constants and indirect bandgap of polycrystalline Al0.25Ga0.75P. Additionally, for wavelengths >500 nm, we find that polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As have the lowest extinction coefficient values when deposited at 420 °C, as opposed to 250 °C. Thus, we hypothesize that the deposition temperature is the most significant factor in dictating the optical constants of these polycrystalline III-Vs. Ultimately, this work demonstrates alternative methods to tune the optical constants of polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As, as opposed to tuning the Al composition.

Enhancing the NIR shielding ability and controlling the surface wettability of RF magnetron sputter deposited WO3-x thin films by tuning the oxygen vacancies

Enhancement in the near-infrared (NIR) shielding property of tungsten oxide (WO3-x, 0 < x < 1) thin films by the induction of further oxygen vacancies via vacuum annealing is discussed in this work. The property is comprehensively analysed by UV–Vis–NIR spectroscopy and variable angle spectroscopic ellipsometry techniques. From transmittance spectra, an average visible transmittance of ∼48% along with an average NIR transmittance of ∼15% (with Tvis/Tsol ratio of 1.49) is obtained for WO3-x thin films vacuum annealed at 500 °C for 1.5 h. The pronounced NIR absorption is attributed to the enhanced polaron absorption and surface plasmon resonance effects produced by the increased oxygen vacancies in the film. In order to realize their potential as energy saving window coatings, thermal shielding test is performed in which vacuum annealed WO3-x thin films could restraint the indoor temperature of the heat box efficiently. X-ray diffractometry, field emission scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy measurements were also performed on the films for elucidating structural, morphological, and compositional characteristics. In addition, contact angle measurements revealed that vacuum annealing could reduce the surface wettability of WO3-x thin films considerably. The present work is significant in the field of development of NIR shielding materials for energy conserving smart window applications, especially for buildings and automobiles.

Optical Properties of Reactive RF Magnetron Sputtered Polycrystalline Cu3N Thin Films Determined by UV/Visible/NIR Spectroscopic Ellipsometry: An Eco-Friendly Solar Light Absorber

Copper nitride (Cu3N), a metastable poly-crystalline semiconductor material with reasonably high stability at room temperature, is receiving much attention as a very promising next-generation, earth-abundant, thin film solar light absorber. Its non-toxicity, on the other hand, makes it a very attractive eco-friendly (greener from an environmental standpoint) semiconducting material. In the present investigation, Cu3N thin films were successfully grown by employing reactive radio-frequency magnetron sputtering at room temperature with an RF-power of 50 W, total working gas pressure of 0.5Pa, and partial nitrogen pressures of 0.8 and 1.0, respectively, onto glass substrates. We investigated how argon affected the optical properties of the thin films of Cu3N, with the aim of achieving a low-cost solar light absorber material with the essential characteristics that are needed to replace the more common silicon that is currently in present solar cells. Variable angle spectroscopic ellipsometry measurements were taken at three different angles, 50∘, 60∘, and 70∘, to determine the two ellipsometric parameters psi, ψ, and delta, Δ. The bulk planar Cu3N layer was characterized by a one-dimensional graded index model together with the combination of a Tauc–Lorentz oscillator, while a Bruggeman effective medium approximation model with a 50% air void was adopted in order to account for the existing surface roughness layer. In addition, the optical properties, such as the energy band gap, refractive index, extinction coefficient, and absorption coefficient, were all accurately found to highlight the true potential of this particular material as a solar light absorber within a photovoltaic device. The direct and indirect band gap energies were precisely computed, and it was found that they fell within the useful energy ranges of 2.14–2.25 eV and 1.45–1.71 eV, respectively. The atomic structure, morphology, and chemical composition of the Cu3N thin films were analyzed using X-ray diffraction, atomic force microscopy, and energy-dispersive X-ray spectroscopy, respectively. The Cu3N thin layer thickness, profile texture, and surface topography of the Cu3N material were characterized using scanning electron microscopy.

Optical method for determining the power spectral density function of randomly rough surfaces by simultaneous processing of spectroscopic reflectometry, variable-angle spectroscopic ellipsometry and angle-resolved scattering data

Optical method for determining the power spectral density function of randomly rough surfaces by simultaneous processing of spectroscopic reflectometry, variable-angle spectroscopic ellipsometry and angle-resolved scattering data

Design and fabrication of color-generating nitride based thin-film optical filters for photovoltaic applications

In this paper, we present the design and fabrication of a 11-layer notch filter for photovoltaic applications. Thickness modulation has been done on a starting quarter-wave design to obtain a 11-layer final structure. For our design parameters, we considered materials with indices of 2.09 and 1.51 as high and low refractive index materials, respectively. Since this filter aims for photovoltaic applications, we defined the substrate as silicon. The design shows a reflection peak of around 73% from 350 to 467 nm with a FWHM of 79 nm along with less than 10% reflection for longer wavelengths of the remaining high transmission region of 300–1200 nm. For fabrication, we used silicon nitride and silicon oxynitride as alternating high and low refractive index materials on a silicon substrate. Layers of silicon nitride and oxynitride were deposited with an electron cyclotron resonance plasma-enhanced chemical vapor deposition reactor and characterized with variable angle spectroscopic ellipsometry and spectrophotometry.

A Low‐Temperature Batch Process for the Deposition of High‐Quality Conformal Alumina Thin Films for Electronic Applications

High‐quality, alumina thin films are extensively used as dielectrics, passivation layers, and barrier layers in electronics and many other applications. However, to achieve optimum stoichiometry and thus performance, the layers are often grown at elevated temperatures (&gt;200 °C) using techniques such as atomic layer deposition (ALD). This is problematic for substrates or structures with low thermal budgets. Herein, alumina thin films are grown on 200 mm silicon substrates employing a versatile deposition method known as MVD at low deposition temperatures (35–150 °C). The chemical composition of the resulting films is investigated postdeposition using X‐ray photoelectron spectroscopy (XPS) and variable angle spectroscopic ellipsometry, with fully stoichiometric Al2O3achieved at deposition temperatures as low as 100 °C. Dielectric measurements confirm outstanding dielectric properties compared to typical thermal ALD layers deposited at much higher temperatures. This low‐temperature deposition performance by considering the MVD reactor design and the “pump‐type” regime of precursor delivery versus the “flow‐type” regime of ALD is rationalized and understood. The results clearly demonstrate that alumina thin films grown with MVD are highly versatile for electronic applications and are of particular relevance and interest for the high‐volume processing of dielectric, passivation, and barrier layers at low temperatures.

Synthesis of 2,5,8-Tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzo[1,2-b:3,4-b′:5,6-b″] Trithiophenes and Their Spontaneous Orientation Polarization in Thin Films

To investigate the relationship between molecular structures and spontaneous orientation polarization (SOP) in organic thin films, 2,5,8-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzo[1,2-b:3,4-b':5,6-b″] trithiophene (TPBTT) and its ethyl derivative (m-ethyl-TPBTT) were synthesized. Variable angle spectroscopic ellipsometry and two-dimensional grazing-incidence wide-angle X-ray scattering showed that the vacuum-deposited films of TPBTT and m-ethyl-TPBTT had a higher degree of molecular orientation parallel to the substrate compared with that of prototypical 2,2',2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) due to the larger π-conjugated benzotrithiophene core. However, TPBTT films showed a lower SOP of +54.4 mV/nm than did the TPBi film (+77.3 mV/nm), indicating that the molecular orientation alone did not determine the SOP. In contrast, m-ethyl-TPBTT showed a larger SOP of +104.0 mV/nm in the film. Quantum chemical calculations based on density functional theory suggested that the differences in the stable molecular conformation and the permanent dipole moments between TPBTT and m-ethyl-TPBTT caused the differences in SOP. These results suggest that the simultaneous control of the orientational order and conformation of the molecules is important to achieving a large SOP in films.

Preparation and application of lysozyme molecularly imprinted surface plasmon resonance biosensors

The aim of this study is to fabricate surface plasmon resonance (SPR) biosensors for real-time detection of protein in complex media. Lysozyme (Lyz) was chosen as a model, and dopamine was used as functional monomer and cross-linker to prepare Lyz surface imprinted SPR biosensors (Lyz-MIPs). Non-covalent interaction was introduced into Lyz-MIPs via a self-assembled monolayer of 3-mercaptopropionic acid to improve the specificity, and protein-resistant poly(2-methyl-2-oxazoline-co-ethylene imine) was also introduced to resist nonspecific adsorption of polydopamine toward proteins in noncavity regions. The prepared Lyz-MIPs biosensor was characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, variable angle spectroscopic ellipsometry, static water contact angle, and zeta potential measurements. SPR adsorption studies were carried out in aqueous Lyz solutions, and the limits of detection and quantification were obtained as 0.19 μg mL−1 and 0.58 μg mL−1, respectively. In addition, Lyz-MIPs biosensor exhibited high selectivity and good reusability. Finally, Lyz-MIPs biosensor was used to detect Lyz in complex media. The recovery of Lyz in simulated egg white was 95.3–105.0%, and 0.23 μg mL−1 Lyz was detected by using Lyz-MIPs biosensor in 20,000 times diluted hen egg white.