Nanoscale Thin Films Research Articles

Synthesis and Sensor Characteristics of Nanoscale Thin Films in the In2O3–SnO2 and Y2O3–TbOx(CeOx) Systems

(In2O3)0.95(SnO2)0.05, (TbOх)0.50(Y2O3)0.50, and (CeO2)0.80(Y2O3)0.20 single-phase cubic solid solution xerogels and nanocrystalline powders have been synthesized via coprecipitation of hydroxides. Using these powders as precursors, nanoscale film electroconductive materials on a corundum substrate have been produced by screen printing. The highest speed of sensor response to ozone is attributed to In0.95Sn0.05O1.5 films, reaching 8–10 s at a temperature of 473 K. (TbOх)0.50(Y2O3)0.50 thin film is found to be sensitive to changes in the concentrations of (CO + CO2) (the sensitivity coefficient S = 25.11) and ozone (S = 3.16–7.94). (CeO2)0.80(Y2O3)0.20 film exhibits a sensor response to (CO + CO2) (S = 3.10). This study opens up the prospects of using the obtained nanopowders and relevant thin films as materials for resistive gas sensors operating at oxygen pressures of 103–104 Pa.

Laser-Driven Phase Segregation and Tailoring of Compositionally Graded Microstructures in Si–Ge Nanoscale Thin Films

The ability to manipulate the composition of semiconductor alloys on demand and at nanometer-scale resolutions is a powerful tool that could be exploited to tune key properties such as the electronic band gap, mobility, and refractive index. However, existing methods to modify the composition involve altering the stoichiometry by temporal or spatial modulation of the process parameters during material growth, limiting the scalability and flexibility for device fabrication. Here, we report a laser processing method for localized tailoring of the composition in amorphous silicon-germanium (a-SiGe) nanoscale thin films on silicon substrates, postdeposition, by controlling phase segregation through the scan speed of the laser-induced molten zone. Laser-driven phase segregation at speeds adjustable from 0.1 to 100 mm s-1 allows access to previously unexplored solidification dynamics. The steady-state spatial distribution of the alloy constituents can be tuned directly by setting the laser scan speed constant to achieve indefinitely long Si1-xGex microstructures, exhibiting the full range of compositions (0 < x < 1). To illustrate the potential, we demonstrate a photodetection application by exploiting the laser-written polycrystalline SiGe microstripes, showing tunability of the optical absorption edge over a wavelength range of 200 nm. Our method can be applied to pseudobinary alloys of ternary semiconductors, metals, ceramics, and organic crystals, which have phase diagrams similar to those of SiGe alloys. This study opens a route for direct laser writing of novel devices made of alloy microstructures with tunable composition profiles, including graded-index waveguides and metasurfaces, multispectral photodetectors, full-spectrum solar cells, and lateral heterostructures.

Effect of Pressure on Boundary Slip of Thin Film Lubrication Using Atomistic Simulation

Mechanical systems on all length scales may be subjected to nanoscale thin film lubrication (TFL). Molecular dynamics (MD) simulations were conducted to investigate the lubrication mechanism and boundary slip of squalane confined in nanogap at 293 K with two different film thicknesses and a wide range of pressures. The molecular distribution, density and velocity profiles of squalane were analyzed. The results show that the lubricant atoms tend to form layers parallel to the wall, but the lubricant molecules orient randomly throughout the film in the directions both parallel and perpendicular to the wall. Most squalane molecules appear twisted and folded, and extend to several atomic layers so that there are no slips between lubricant layers. The distances between the lubricant layers are irregular rather than broadening far away from the walls. The boundary slip at the interface of bcc Fe (001) and squalane only occurs at high pressure because of the strong nonbond interactions between lubricant atoms and wall atoms. The tendency of boundary slip is more obvious for films with thinner film thickness. According to the simulations, the relationship between the slip length and the pressure is given.

Leakage current lowering and film densification of ZrO2 high-k gate dielectrics by layer-by-layer, in-situ atomic layer hydrogen bombardment

A layer-by-layer, in-situ H2 plasma treatment in each cycle of atomic layer deposition, referred to as “atomic layer hydrogen bombardment” (ALHB), is applied to improve electrical properties of ZrO2 high-k gate dielectrics. The H2 plasma bombardment facilitates the adatom migration due to energy delivery to each as-deposited monolayer from the H2 plasma. In addition, the H2 plasma treatment contributes to the removal of precursor ligands for the release of steric hindrance. Hence the ALHB treatment leads to film densification and suppression of oxygen vacancies of ZrO2, as evidenced by X-ray reflectivity and X-ray photoelectron spectroscopy characterizations. As a result, ~90% decrease of gate leakage current is achieved in the ZrO2 high-k gate dielectrics with capacitance equivalent thicknesses of ~1.3 nm and ~0.6 nm in metal-insulator-semiconductor and metal-insulator-metal capacitors, respectively. The results manifest that the ALHB treatment is a promising technique to enhance dielectric and electrical characteristics of nanoscale thin films, for further progress of advanced devices such as sensors, solar cells, memories, and nanoelectronics.

Pulsed Electrodeposition of Ultrathin Polyaniline Films and Mechanistic Understanding of their Anion-Mediated Electrochemical Behavior

Electrode materials which undergo anion insertion are of interest for next-generation energy storage devices and electrochemical water desalination. Polyaniline (PANI) is a robust and well-studied electrode material for anion insertion, but to date we have been unable to establish the electrochemical and anion-binding performance of PANI at nanoscale thicknesses because these thicknesses are not obtainable using standard PANI deposition procedures. Here, we report a new pulsed electrodeposition procedure for the controlled growth of PANI thin films with nanometer-scale thickness control. Using this pulsing technique, we deposit nanoscale (<100 nm) thin films of PANI onto stainless steel (SS) disks and gold electrochemical quartz crystal microbalance (EQCM) crystals. We examine the charge rate and anion-binding properties as a function of nanoscale thickness, and reveal previously undescribed insights into the charge storage and anion binding mechanisms of PANI. In particular, we identify that PANI films of <10 nm thickness provide rapid chloride ion uptake for desalination applications, and that thicker ∼100 nm PANI films are able to achieve rapid charge storage in sulfate solutions due to SO42−/HSO4− embedded within the PANI acting as a proton donor/acceptor. The results we report will inform the use of PANI thin films for energy storage and desalination applications.

Dielectric properties and reliability enhancement of atomic layer deposited thin films by in situ atomic layer substrate biasing

The dielectric and physical properties of nanoscale thin films are significantly enhanced by atomic layer substrate biasing.

Behavior of Solutions to a Fourth-Order Nonlinear Parabolic Equation with Logarithmic Nonlinearity

This paper deals with a class of fourth-order parabolic equations modeling the evolution of the epitaxial growth of nanoscale thin films. By exploiting the variational structure of the equation, the logarithmic Sobolev inequality and a family of potential wells, the conditions on existence of global and infinite time blow-up solutions are obtained. Moreover, the finite time extinction and exponential decay of the solutions are also discussed.

Synthesis of 5,8-Dimethyl-Dibenzo[b,j][1,10]Phenanthroline and Its Ru Complex

A convenient, two-step synthesis of the 5,8-dimethyl-dibenzo[b,j][1,10]phenanthrolines is presented. The first step is a Buchwald-Hartwig amination of 1,2-dibromobenzene and 2’-Aminoacetophenone to produce 1,1’-((1,2-phenylenebis(azanediyl))bis(2,1-phenylene))bis(ethan-1- one), which is converted to the final product via a ring-closing reaction. The overall reaction yield is 63%. The complexation of 5,8-dimethyldibenzo[b,j][1,10]phenanthrolines with 2,2’-bipyridine-4,4’-dicarboxylic acid (dcbpy) and Ru Ru(DMSO)4Cl2 is also reported and the Ru complex might be used to prepare a nanoscale thin film for dye-sensitives solar cell and other optoelectronic devices.

Quantum model for the effect of thiols adsorption on resistivity of gold ultrathin films

The predominant role of surface scattering, in electronic transport through nanoscale thin films, was examined by measuring and modeling the change in resistivity induced by the adsorption of thiols on the surface. For this purpose, gold ultrathin films on sapphire, using chromium as surfactant, were prepared through thermal evaporation, seeking to maximize the surface induced dispersion. A maximum resistivity increase of 13.5% was observed, in an 8 nm Au/Cr/Sapphire sample. This is the highest reported value for such films to date. The morphology of the samples was measured by STM and characterized through height-difference correlation function. A fractal self-affine representation of the surface was found, and it was modified to account the thiol effect: the scattering center due to the adsorption of a molecule was modeled as a void in the surface. This change was related to the electrical transport of the film through two quantum models: the Palasantzas and Barnas (PB) theory and the Sheng, Xing and Wang theory, extended by Munoz et al. (mSXW). For our samples, the mSXW theory did not predict a resistivity change, while the PB theory provides a good description of the experimental resistivity increase due to thiols adsorption as function of thickness.

Numerical Schemes for Solving the Time-Fractional Dual-Phase-Lagging Heat Conduction Model in a Double-Layered Nanoscale Thin Film

This article proposes a time fractional dual-phase-lagging (DPL) heat conduction model in a double-layered nanoscale thin film with the temperature-jump boundary condition and a thermal lagging effect interfacial condition between layers. The model is proved to be well-posed. A finite difference scheme with second-order spatial convergence accuracy in maximum norm is then presented for solving the fractional DPL model. Unconditional stability and convergence of the scheme are proved by using the discrete energy method. A numerical example without exact solution is given to verify the accuracy of the scheme. Finally, we show the applicability of the time fractional DPL model by predicting the temperature rise in a double-layered nanoscale thin film, where a gold layer is on a chromium padding layer exposed to an ultrashort-pulsed laser heating.

Influence of Hydrocarbon Base Oil Molecular Structure on Lubricating Properties in Nano-scale Thin Film

In nano-scale thin film, the lubricant molecular structure may have more significant impact to lubricating performance than in bulk states. In order to investigate the influence of hydrocarbon base oil molecular structure to lubricating properties, three base oil samples with different molecular structure were synthesized in this study, the molecular structure was detected. Film thickness and friction coefficient were measured by EHD2 ultra thin film measurement system, and wear scar was evaluated by four-ball tester. The base oil with linear molecular structure show lower film thickness and friction coefficient, even the base oil has higher viscosity and viscosity index than other samples, while the branched structure makes the molecule more rigid than linear one, which increase the film thickness and friction coefficient. The linear molecules with high viscosity index sustained oil film at high temperature, which reduced the wear scar.

Sealing Performance Evaluation Method of Nano-scale Magnetic Thin Film Materials in Marine Tanks

Wang, S.; Jiang, J., and Cao, W., 2019. Sealing performance evaluation method of nano-scale magnetic thin film materials in marine tanks. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 941–946. Coconut Creek (Florida), ISSN 0749-0208.In order to evaluate the sealing performance of nano-scale magnetic thin film materials in marine tanks, a method for evaluating the sealing performance of nano-scale magnetic thin film materials in marine tanks based on spatial visual image feature extraction is proposed. The differential frame point scanning and spatial vision high resolution imaging analysis method are used to collect the image information of ship tank nano-scale magnetic thin film material. The sealing gap of ship tank nano-scale magnetic film material, the weakening of material mechanics, the sealing frame point and other parts of the three-dimensional frame structure reconstitute image modeling. The edge structure feature decomposition and texture segmentation of ship tank nanoscale magnetic film material images are carried out. The stress fitting model of structural seal gap of ship tank nano-scale magnetic film material is constructed. The feature point extraction and mechanical state dynamic estimation of ship tank nano-scale magnetic film material seal gap are carried out by using three-dimensional frame structure reconstruction image feature extraction method, and the accurate prediction and evaluation of seal gap state of ship tank nano-scale magnetic film material seal are realized. The simulation results show that the sealing performance of nano-scale magnetic thin film material in ship tank is tested by this method, and the positioning accuracy of sealing gap point of nano-scale magnetic thin film material in ship tank is higher, the reliability index of closed performance evaluation is better, and the failure probability is the smallest.

Growth of Hybrid Inorganic/Organic Chiral Thin Films by Sequenced Vapor Deposition.

One of the many challenges in the study of chiral nanosurfaces and nanofilms is the design of accurate and controlled nanoscale films with enantioselective activity. Controlled design of chiral nanofilms creates the opportunity to develop chiral materials with nanostructured architecture. Molecular layer deposition (MLD) is an advanced surface-engineering strategy for the preparation of hybrid inorganic-organic thin films, with a desired embedded property; in our study this is chirality. Previous attempts to grow enantioselective thin films were mostly focused on self-assembled monolayers or template-assisted synthesis, followed by removal of the chiral template. Here, we report a method to prepare chiral hybrid inorganic-organic nanoscale thin films with controlled thickness and impressive enantioselective properties. We present the use of an MLD reactor for sequenced vapor deposition to produce enantioselective thin films, by embedding the chirality of chiral building blocks into thin films. The prepared thin films demonstrate enantioselectivity of ∼20% and enantiomeric excess of up to 50%. We show that our controlled synthesis of chiral thin films generates opportunities for enantioselective coatings over various templates and 3D membranes.

Strong Opto-Structural Coupling in Low Dimensional GeSe3 Films.

Chalcogenide glasses as nanoscale thin films have become leading candidates for several optical and photonic technologies, ranging from reflective displays and filters to photonic memories. Current material systems, however, show strong optical absorption which limits their performance efficiencies and complicates device level integration. Herein, we report sputter deposited thin films of GeSe3, which are low loss and in which the flexible nature of the atomic structure results in thermally activated tunability in the refractive index as well as in the film's physical volume. Such changes, which occur beyond a threshold temperature are observed to be accumulative and directed toward a more equilibrium amorphous state of the film, instead of crystallization. Our results provide insight into a new type of configurability that is based on strong coupling in the material's opto-structural properties. The low optical losses in this material system combined with the tunability in the optical properties in the visible and near-infrared have direct application in higher performing optical coatings and in corrective optics.

Femtosecond Laser-Excitation-Driven High Frequency Standing Spin Waves in Nanoscale Dielectric Thin Films of Iron Garnets.

We demonstrate that femtosecond laser pulses allow triggering high-frequency standing spin-wave modes in nanoscale thin films of a bismuth-substituted yttrium iron garnet. By varying the strength of the external magnetic field, we prove that two distinct branches of the dispersion relation are excited for all the modes. This is reflected in particular at a very weak magnetic field (∼33 mT) by a spin dynamics with a frequency up to 15GHz, which is 15 times higher than the one associated with the ferromagnetic resonance mode. We argue that this phenomenon is triggered by ultrafast changes of the magnetic anisotropy via laser excitation of incoherent and coherent phonons. These findings open exciting prospects for ultrafast photo magnonics.

Design, characterization and optical properties of assembled nanoscale thin films of copper (II) complex with 5-azo-Phenol-8-Hydroxyquinoline

The nano-sized organic and inorganic materials are opening pathways for chemical flexible composites that exhibits high advantage in their optical, electrical and mechanical properties. The present work reports the syntheses of nano-sized Cu(II) complex of 5-azo-phenol-8-hydroxyquinoline (NS Cu(II)-(5AP-8HQ)) thin films on glass and quartz substrates, using static layer by layer soft surface reaction (LBL) technique. The NS Cu(II)-(5AP-8HQ) thin films were characterized using Fourier transform infrared (FT-IR), thermal gravimetric analysis (TGA), high resolution-transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). The optical transmittance and optical reflectance were measured at the wavelength range between 200 and 2500 nm. The optical transition was characterized by direct allowed transition with an optical energy gap of about 4.59 eV. The existence of Cu2+ and the phenolate group acted to decrease the valence band and consequently increase the energy gap. Also, the refractive index for NS Cu(II)-(5AP-8HQ) showed a thickness dependence and was found to be 2.6 at wavelength equal to 1000 nm. The nonlinear refractive index and nonlinear optical susceptibility were calculated and the effect of material thickness on the optical constants was also discussed as well.

Modulation of ferroelectricity and antiferroelectricity of nanoscale ZrO2 thin films using ultrathin interfacial layers

In this study, tailoring the microstructures and ferroelectric(FE)/antiferroelectric(AFE) properties of nanoscale ZrO2 thin films is demonstrated with an intentional introduction of sub-nanometre interfacial layers. The ferroelectricity of ZrO2 thin films is significantly enhanced by the HfO2 interfacial layers, while the TiO2 interfacial layers lead to a dramatic transformation of ZrO2 from ferroelectricity into antiferroelectricity. The HfO2 and TiO2 interfacial layers boost the formation of the polar orthorhombic phase with (111)-texture and the non-polar tetragonal phase with (110)-texture in the FE/AFE ZrO2 thin films, respectively, as evidenced by grazing incidence, out-of-plane, and in-plane X-ray diffraction measurements. Furthermore, the modulation of ferroelectricity and antiferroelectricity of nanoscale ZrO2 thin films by the HfO2/TiO2 interfacial layers can be achieved without high-temperature annealing, which is highly advantageous to process integration. The findings demonstrate the important role of the interfaces in the effective tuning of FE/AFE properties of nanoscale thin films.

Backscattering Immunity of Dipole-Exchange Magnetostatic Surface Spin Waves.

The existence of backscattering-immune spin-wave modes is demonstrated in magnetic thin films of nanoscale thickness. Our results reveal that chiral magnetostatic surface waves (CMSSWs), which propagate perpendicular to the magnetization direction in an in-plane magnetized thin film, are robust against backscattering from surface defects.CMSSWs are protected against various types of surface inhomogeneities and defects as long as their frequency lies inside the gap of the volume modes. Our explanation is independent of the topology of the modes and predicts that this robustness is a consequence of symmetry breaking of the dynamic magnetic fields of CMSSWs due to the off-diagonal part of the dipolar interaction tensor, which is present both for long- (dipole-dominated) and short-wavelength (exchange-dominated) spin waves. Micromagnetic simulations confirm the robust character of the CMSSWs. Our results open a new direction in designing highly efficient magnonic logic elements and devices employing CMSSWs in nanoscale thin films.

Global Existence, Finite Time Blow-Up, and Vacuum Isolating Phenomenon for a Class of Thin-Film Equation

We consider a thin-film equation modeling the epitaxial growth of nanoscale thin films. By exploiting the boundary conditions and the variational structure of the equation, we look for conditions on initial data that ensure the solution exists globally or blows up in finite time. Moreover, for global solution, we establish the exponential decays of solutions and energy functional, and give the concrete decay rate. As for blow-up solution, we prove that the solution grows exponentially and obtain the behavior of energy functional as t tends to the maximal existence time. Under the low initial energy, we get further two necessary and sufficient conditions for the solution existing globally and blowing up in finite time, respectively. A new sufficient condition such that the solution exists globally is obtained; we point out that this initial condition is independent to initial energy. Finally, we discuss the vacuum isolating phenomena of the solution.

Elastic property characterization of soft substrate-supported thin films using multiscale digital image correlation

We present an original experimental approach to characterizing the Young’s modulus of nanoscale thin films on a soft substrate. A microtester is developed to permit pre-stretching of the polymer substrate and symmetric film deposition on both sides of its half surface. During compression and tensile tests related to the as-deposited residual stress state, the full-field macrostrains of the film-substrate composite and the uncoated substrate can be measured simultaneously with the film microstrains using multiscale digital image correlation. The macrostrain difference allows extraction of the elastic properties of thin films. Combined with microstrains, a perfect strain transfer at the film-substrate interface, minus buckling of the composite, is evidenced. No film delamination or cracking phenomena are observed, and the measured Young’s modulus agrees well with the literature. Our approach could potentially be used to explore the mechanical properties and behaviors of emerging functional thin films, both crystalline and amorphous.