Ellipsometry Of Thin Films Research Articles

Wide-Spectrum Ellipsometry Measurement Based on Two Parallel Channels

To solve the problem of a single light source, phase compensator, and detector, amongst others—which cannot meet the ellipsometry measurement requirements over a wide spectral range (from visible light (VIS) to short-wave infrared (SWIR) and even mid infrared (MIR; 400–3200 nm))—a wide-spectrum thin-film ellipsometry measurement solution based on two parallel channels was proposed. Full spectral coverage was achieved through a combination of the VIS-SWIR (400–2100 nm) and SWIR-MIR (2100–3200 nm) dual-band ellipsometry—that is, the ellipsometry measurements in the VIS-SWIR and SWIR-MIR bands were integrated in the same system. Consequently, the ellipsometry parameters for full spectral coverage could be obtained using a single measurement. An SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin-film sample on a Si substrate of thickness 103.2 nm was used to evaluate the proposed ellipsometry system. The results showed that the thin-film thickness measurement accuracy was high (±0.5 nm in the range of 400–3200 nm), the thickness repeatability measurement accuracy was 0.03 nm, the refractive index repeatability measurement accuracy was 0.003, and the measurement time was approximately 0.5 s/λ, the proposed system having the advantages of high integration, simple operation, and high measurement speeds.

Ellipsometry of thin films of biological objects under conditions of total internal reflection

An analysis of the ellipsometric parameters of the reflected light from the prism test material air system is carried out when circularly polarized light is incident on it under the conditions of the onset of the phenomenon of total internal reflection. At the onset of total internal reflection, the ellipsometry parameter shows high variability with the angle of incidence, in contrast to the parameter r0. It is shown that TIR occurs when the angle of incidence is not equal to the critical angle of the adjacent media for two different materials, these angles differ from each other. In the case of a film, the TIR phenomenon occurs at an angle equal to the critical angle at the prism-air interface and does not depend on the film material. The results obtained show the high efficiency of using the ellipsometric method together with circularly polarized incident radiation for diagnostics of thin films made of biological material.

Effect of air mass on carrier losses in bifacial silicon heterojunction solar cells

We investigate the effect of incident spectra on current loss as a function of depth and voltage into high efficiency textured bifacial silicon heterojunction solar cells. We integrate thin-film ellipsometry measurements with a 3D optical model and a 2D electronic model and validate our model with measurements of external quantum efficiency and Suns-Voc. For front illumination at normal incidence, an increasing air mass of AM1.5 to 10 reduces current density loss due to parasitic absorption in ITO and a-Si:H from 8.1% to 4.0%, and increases recombination loss at maximum power from 4.2% to 4.7%, resulting in an overall increase in collected current (88.2% to 90.5%). Cell performance metrics are summarized as a function of air mass, with efficiency peaking at AM5.0 for front illuminated and rear illuminated cells with an albedo of unity. We further demonstrate the impact of spectra on bifacial efficiency by calculating rear-side performance with the spectral albedo of dry grass. Overall, current-collection and efficiency trends emphasize the importance of considering spectral effects in energy yield models. These results are of particular importance for cell structures with high bifaciality and significant spectral albedo contributions, locations with large proportions of diffuse light, and high air mass locations as in mid-to-high latitudes. • Optoelectronic model is validated with measurements of EQE and Suns-Voc. • Collected photogenerated current increases from 88% to 91% between AM1-10. • Maximum cell efficiency occurs at AM5 but is heavily influenced by spectral albedo. • Encapsulation increases parasitic absorption, decreasing efficiency by 1.4% abs. • Most impactful for modules with high bifaciality, high albedo, mid to high latitude.

Membrane-Based In Situ Mid-Infrared Spectroscopic Ellipsometry: A Study on the Membrane Affinity of Polylactide-co-glycolide Nanoparticulate Systems.

Mid-infrared (IR) ellipsometry of thin films and molecule layers at solid–liquid interfaces has been a challenge because of the absorption of light in water. It has been usually overcome by using configurations utilizing illumination through the solid substrate. However, the access to the solid–liquid interface in a broad spectral range is also challenging due to the limited transparency of most structural materials in the IR wavelength range. In this work, we propose a concept of a microfabricated analysis cell based on an IR-transparent Si membrane with advantages of a robust design, flexible adaptation to existing equipment, small volume, multiple-angle capabilities, broad wavelength range, and opportunities of multilayer applications for adjusted ranges of high sensitivity. The chamber was prepared by 3D micromachining technology utilizing deep reactive ion etching of a silicon-on-insulator wafer and bonded to a polydimethylsiloxane microfluidic injection system resulting in a cell volume of approximately 50 μL. The mechanical stability of the 2 and 5 μm-thick membranes was tested using different “backbone” reinforcement structures. It was proved that the 5 μm-thick membranes are stable at lateral cell sizes of 5 mm by 20 mm. The cell provides good intensity and adjustment capabilities on the stage of a commercial mid-IR ellipsometer. The membrane configuration also provides optical access to the sensing interfaces at a broad range of incident angles, which is a significant advantage in many potential sensing structure configurations, such as plasmonic, multilayer, 2D, or metamaterial applications.

Reversible Hydration of CH3NH3PbI3 in Films, Single Crystals, and Solar Cells

Solar cells composed of methylammonium lead iodide perovskite (MAPI) are notorious for their sensitivity to moisture. We show that (i) hydrated crystal phases are formed when MAPI is exposed to water vapor at room temperature and (ii) these phase changes are fully reversed when the material is subsequently dried. The reversible formation of CH3NH3PbI3·H2O followed by (CH3NH3)4PbI6·2H2O (upon long exposure times) was observed using time-resolved XRD and ellipsometry of thin films prepared using “solvent engineering”, single crystals, and state-of-the-art solar cells. In contrast to water vapor, the presence of liquid water results in the irreversible decomposition of MAPI to form PbI2. MAPI changes from dark brown to transparent on hydration; the precise optical constants of CH3NH3PbI3·H2O formed on single crystals were determined, with a bandgap at 3.1 eV. Using the single-crystal optical constants and thin-film ellipsometry measurements, the time-dependent changes to MAPI films exposed to moisture were m...

ブリルアン振動を用いた酸化物薄膜の弾性定数測定と組織評価

This paper studies the elastic constant and microstructure of amorphous SiO_2 (a-SiO_2) thin films deposited on Si substrates. a-SiO_2 thin films were prepared by the reactive sputtering with a Si target in the argon/oxygen mixture gas. We measured the Brillouin-oscillation frequency using a femtosecond pump-probe method. We determined the longitudinal-wave elastic constant from the measured frequency and the refractive index measured by the thin-film ellipsometry. The results show that the elastic constant of the a-SiO_2 thin film highly depend on the microstructure and microcracks. The micromechanics model was developed to explain the decrease of the stiffness with thin pancake-shaped microcracks, which were randomly distributed in the a-SiO_2 matrix. This study demonstrates that the Brillouin oscillation technique is an effective tool for evaluation of not only acoustic properties but also reliability of transparent materials.

Control of DNA incorporation into nanoparticles with poly(L-lysine) multilayers

Nanoparticles coated with DNA and poly(L-lysine) (PLL) were prepared using a layer-by-layer assembly technique under various solution conditions. Both the level of DNA loading into the materials, the rate and the extent of DNA released from films upon degradation were controlled by varying the pH of polyelectrolyte assembly solutions. To determine optimal conditions for DNA loading, analogous films assembled on flat surfaces were prepared under various pH conditions. Using UV–vis spectroscopy and thin-film ellipsometry, it was found that the extent of DNA incorporation could be varied by more than a factor of two, and that the highest loading was obtained for films built using a combination of DNA and poly(L-lysine) solutions of pH = 4 and pH = 7, respectively. The layers coated onto the silica nanoparticles permitted the surface charge to be characterized by zeta potential electrophoresis. Furthermore, the acid–base dissociation constant measured for PLL on the outermost layer of the DNA/PLL film showed that the pKaof PLL can be shifted by more than three units. Film degradability was investigated via the exposure of films assembled under different pH conditions to α-chymotrypsin. The fraction of DNA released from degraded films can also be increased by a factor of three when films are built under conditions of pH = 4 for the DNA solution. The resultant effect on the transfection ability of pEGFP-N1/PLL coated particles was then measured, and results suggest that the control achieved over the bulk film properties also extends to a strong influence on cell uptake and transfection.Key words: polyelectrolyte multilayer, DNA incorporation, enzymatic degradation, nanoparticles, gene therapy.

Spot focus size effect in spectroscopic ellipsometry of thin films

A focused as opposed to collimated light beam is typically used as probe in order to achieve a smaller as well as more intense light interrogation area in spectroscopic ellipsometry of thin films. In this work, we performed geometric ray analysis at the illumination and recording ends of such a system. The numerical results revealed substantial changes in (i) average optical path length and (ii) optical path length differences, which varied according to wavelength despite the film thickness remaining uniform. These results were able to consistently explain the anomalies found when different focus probe beam sizes were used in experimental spectroscopic ellipsometry measurements.

Envelope analysis in spectroscopic ellipsometry of thin films. Application to a weakly-absorbing polymer film

The envelope technique is a powerful analytical tool already known in spectrophotometry, but only recently introduced in ellipsometry. We will develop its formalism for tan ψ in weakly absorbing interference films and see how data extraction can be greatly simplified. The envelope technique permits to separate the extraction of the refractive index of the film from the thickness. Therefore, it is ideal for those moderately thick films affected by multivalued solutions in conventional regressions, typically in polymer film preparations. We present some experimental results for a photolithographic resin deposited on glass.

Spectroscopic ellipsometry of non-absorbing films independent of film thickness

Spectroscopic ellipsometry of thin films frequently encounter the problem of multi-valued solutions in a regression fit. A good starting thickness value is critical to reach the correct solution. We present a formulation to extract optical parameters from film–substrate systems and spectroscopic ellipsometry independently of the film thickness d. We do not need to include it as a parameter in a regression fit. The basic idea is to use the envelopes of tan ψ curves instead of the curves itself. This approach simplifies the analysis efficiently. The envelope analysis is thickness-independent. As we have two envelopes, we may extract two optical constants, and by also using the points touching the envelopes (the envelope-extremes) we may extract the thickness separately. We develop and apply the formulation for non-absorbing media and we also check its validity for absorbing substrates. Another important conclusion derived from the results is that the refractive index of the film can be obtained even if the substrate is unknown.

Transmission and reflection ellipsometry of thin films and multilayer systems

Ellipsometric studies are generally carried out in the reflection mode rather than in the transmission mode, requiring invariably opaque substrates or substrates in which the backreflection is minimized or suppressed by different methods. In the present research we used a transmission and reflection photoellipsometry method to study electrochromic materials and their multilayer systems deposited on thick substrates. The role of the substrate is examined carefully, and the contributions from multiple reflections in the substrate are taken into account in the theoretical treatment. This procedure not only allows the study of thin films deposited on quasi-transparent substrates, but when carried out in conjunction with reflection measurements it greatly improves the accuracy in the determination of the optical constants. Optical measurements are carried out on an automatic reflection transmission spectroscopic ellipsometer. Solid-state ionic materials used in electrochromic systems such as indium tin oxide, tungsten oxide, and their multilayer structures deposited on glass substrates are used as examples. A software based on the above theory, optikan, was developed to model and analyze such systems. It is demonstrated that the photoellipsometry method proposed is especially suited to analyzing electrochromic materials and transmitting devices in a nondestructive way.

Thin film ellipsometry at a photon energy of 97eV

We report the first multiple angle of incidence ellipsometry in the Extreme Ultra-Violet region. Extreme sensitivity to sub-atomic size of the relative amplitude attenuation of a thin film sample is evident. A large variation of the states of polarization was observed as the angle of incidence was varied. Best fit analysis with a model of a single layer with rough boundaries shows that EUV ellipsometry is sensitive enough to resolve the refractive index of 0.001 and the thickness of 0.1nm.

Strain induced anisotropy in As_2S_3, As_2Se_3, and ZnSe films on KCl substrates via 106-μm and 06328-μm ellipsometer measurements and 06328-μm reflector measurements

Ellipsometric measurements at 10.6 microm using a modulated light ellipsometer and ellipsometer and reflectometer measurements at 0.6328 microm are reported for the refractive indices of As(2)S(3), As(2)Se(3), and ZnS films deposited on KCl substrates. The observation of strain-induced anisotropy is reported, and an analysis of the effects of anisotropy in thin film ellipsometry is presented.

Ellipsometry of thin films of copper phthalocyanine

Ellipsometric measurements have provided qualitative information on the optical properties of CuPC films deposited on a thin gold layer substrate. Detailed interpretation was complicated by variations in the density of the deposited layers and the surface roughness of the substrate. Films less than 100 nm thick can be satisfactory represented by a single homogeneous isotropic layer. Thicker films appear to be equivalent to an isotropic inner layer and an anisotropic outer layer, where the latter results from bulk deposition of CuPC with the molecules in a predominant orientation to the surface. Reasonable agreement has been obtained between film thicknesses measured by weighing and by ellipsometry, assuming a single homogeneous anisotropic film for thickness in excess of 150 nm.

Combined reflection and transmission thin-film ellipsometry: a unified linear analysis

A scheme of combined reflection and transmission ellipsometry on light-transmitting ambient-film-substrate systems is proposed and the required sample design and instrument operation are investigated. A comparative study of the sensitivity of external and internal reflection and transmission ellipsometry is carried out based on unified linear approximations of the exact equations. These approximations are general in that an arbitrary initial film thickness is assumed. They are simple, because a complex sensitivity function is introduced whose real and imaginary projections determine the psi (Psi) and delta (Delta) sensitivity factors. Among the conclusions of this paper are the following. (1) External reflection ellipsometry near the Brewster angle of a transparent ambient-substrate system is extremely sensitive to the presence of very thin interfacial films. For example, films as thin as 10(-5) A of gold are readily detectable on glass substrates at an angle of incidence 0.3 degrees below the Brewster angle, assuming a measuring wavelength of 5461 A with an ellipsometer of 0.05 degrees precision. (2) The formation of thin nonabsorbing films at the interface between transparent ambient and substrate media is not detectable, to first order, as a change in the ellipsometric angle Psi by either internal or external reflection or transmission ellipsometry. (3) The film-detection sensitivity of transmission ellipsometry increases monotonically with angle of incidence. (4) For each angle of external incidence there is a corresponding angle of internal incidence that leads to the same values of the reflection and transmission sensitivity functions. These angles are interrelated by Snell's law. (5) The ranges of validity of the linear approximation in reflection and transmission ellipsometry are comparable. The case of total internal reflection ellipsometry may lead to strong nonlinear behavior of Psi and Delta as functions of the film thickness in the range below 0.05 of the wavelength of light.