Extraction of interface stiffness in superlattices : Proposal of the interface elasticity parameter

We develop a methodology to extract the interface stiffness in superlattices using picosecond ultrasound spectroscopy. Ultrafast light pulses excite and detect thickness phonon modes in a five-layered superlattice thin film, consisting of three matrix layers and two ultrathin interlayers. The thickness of interlayer is varied between 2 and 10 -A. We define the interface elasticity parameter as the frequency ratio of two phonon modes, which are sensitive and insensitive to the interface elastic constants, and inversely evaluated the elastic stiffness of the interlayer. It is revealed that the interface in the superlattice thin film is significantly softened.Hirotsugu Ogi, Tomohiro Shagawa, Nobutomo Nakamura and Masahiko Hirao. Extraction of interface stiffness in superlattices : Proposal of the interface elasticity parameter. Applied Physics Express, 2009, 2(10), 105001. https://doi.org/10.1143/APEX.2.105001

Relationship between viscosity change and specificity in protein binding reaction studied by high-frequency wireless and electrodeless MEMS biosensor

This study proposes a methodology for evaluating specific binding behavior between proteins using a resonance acoustic microbalance with a naked-embedded quartz (RAMNE-Q) biosensor. We simultaneously measured the frequency responses of fundamental (58 MHz) and third-order (174 MHz) modes during multi step injections of proteins and deduced the thickness and viscosity evolutions of the protein layer. The viscosity increases with the progress of the binding reaction in nonspecific binding, but it markedly decreases in specific-binding cases. Thus, the high-frequency RAMNE-Q biosensor can be a powerful tool for evaluating specificity between proteins without measuring dissipation.Tomohiro Shagawa, Hiroomi Torii, Fumihito Kato, Hirotsugu Ogi and Masahiko Hirao. Relationship between viscosity change and specificity in protein binding reaction studied by high-frequency wireless and electrodeless MEMS biosensor. Japanese Journal of Applied Physics, 2015, 54(6), 068001. https://doi.org/10.7567/JJAP.54.068001

Viscoelasticity evolution in protein layers during binding reactions evaluated using high-frequency wireless and electrodeless quartz crystal microbalance biosensor without dissipation

In this study, we demonstrate the effectiveness of a resonance acoustic microbalance with a naked embedded quartz (RAMNE-Q) biosensor for evaluating viscoelastic property changes in thin protein layers during protein deposition reactions without dissipation measurement. Quartz crystal microbalance (QCM) biosensors have conventionally been adopted for the viscoelasticity evaluation of adsorbed protein layers by measuring dissipation as well as resonance frequency. However, dissipation, or the vibrational energy loss, is easily affected by many factors and is rarely measured with sufficiently high accuracy. To evaluate viscoelasticity only from a reliable frequency response, one needs to perform an ultrahighfrequency measurement, which is here achieved using the RAMNE-Q biosensor. Simultaneous frequency measurement is performed for fundamental and overtone modes up to 406MHz of a 58MHz RAMNE-Q biosensor during various binding reactions, and evolutions of viscosity, shear modulus, and thickness of adsorbed protein layers are inversely evaluated. A marked difference is observed in the viscosity evolution between specific and nonspecific binding reactions. Furthermore, the reversed frequency response appears, which indicates the modification of the protein structure into a rigid structure.Tomohiro Shagawa, Hiroomi Torii, Fumihito Kato, Hirotsugu Ogi and Masahiko Hirao. Viscoelasticity evolution in protein layers during binding reactions evaluated using high-frequency wireless and electrodeless quartz crystal microbalance biosensor without dissipation. Japanese Journal of Applied Physics, 2015, 54(9), 096601. https://doi.org/10.7567/JJAP.54.096601

Elastic-constant measurement in oxide and semiconductor thin films by Brillouin oscillations excited by picosecond ultrasound

In this study, an elastic-stiffness evaluation in transparent or translucent thin films using Brillouin oscillations detected by picosecond ultrasound is conducted. An ultrahigh-frequency (≥50 GHz) strain pulse is generated using femtosecond light pulse in specimens and propagates in the film-thickness direction. The time-delayed probe light pulse enters the specimen, which is diffracted by the strain pulse, causing oscillations in the reflectivity change of the probe light pulse. The oscillation frequency gives the elastic modulus with ellipsometry for refractive index. The theoretical calculation predicts the accuracy of stiffness measurement. The methodology is applied to the study of amorphous silica, amorphous tantalum oxide, diamond thin films, and silicon wafers.Hirotsugu Ogi, Tomohiro Shagawa, Nobutomo Nakamura, Masahiko Hirao, Hidefumi Odaka and Naoto Kihara. Elastic-constant measurement in oxide and semiconductor thin films by Brillouin oscillations excited by picosecond ultrasound. Japanese Journal of Applied Physics, 2009, 48(7S), 07GA01. https://doi.org/10.1143/JJAP.48.07GA01