Micro-Raman measurement of strain in silicon nanowires

Crystalline nanostructures such as silicon nanowires (SiNWs) may have residual mechanical stress and strain from the fabrication process, which can potentially impair their reliability as building blocks of Microelectromechanical system (MEMS). The amount of strain may be minuscule, which requires very accurate measurements to determine the strain. Micro-Raman spectroscopy is a work horse tool since it is a simple, fast and nondestructive technique that can be used to assess mechanical strain. However, a precise evaluation of residual strain for nanostructures using micro-Raman spectroscopy requires careful calibrations and theoretical calculations. This thesis describes the interrelations between Raman shift and strain in fabricated silicon nanowires. The calibration methods are used to eliminate the two dominant errors: errors in focusing, and laser heating effects, which can lead to apparent Raman shifts. Finally, the Raman measurement results are discussed and the corresponding residual strain in the [110] direction is calculated. This work is concluded with the discussion of possible causes of strain

Analysis of a Casimir-driven parametric amplifier with resilience to Casimir pull-in for MEMS single-point magnetic gradiometry

The Casimir force, a quantum mechanical effect, has been observed in several microelectromechanical system (MEMS) platforms. Due to its extreme sensitivity to the separation of two objects, the Casimir force has been proposed as an excellent avenue for quantum metrology. Practical application, however, is challenging due to attractive forces leading to stiction and device failure, called Casimir pull-in. In this work, we design and simulate a Casimir-driven metrology platform, where a time-delay-based parametric amplification technique is developed to achieve a steady-state and avoid pull-in. We apply the design to the detection of weak, low-frequency, gradient magnetic fields similar to those emanating from ionic currents in the heart and brain. Simulation parameters are selected from recent experimental platforms developed for Casimir metrology and magnetic gradiometry, both on MEMS platforms. While a MEMS offers many advantages to such an application, the detected signal must typically be at the resonant frequency of the device, with diminished sensitivity in the low frequency regime of biomagnetic fields. Using a Casimir-driven parametric amplifier, we report a 10,000-fold improvement in the best-case resolution of MEMS single-point gradiometers, with a maximum sensitivity of 6 Hz/(pT/cm) at 1 Hz. Further development of the proposed design has the potential to revolutionize metrology and may specifically enable the unshielded monitoring of biomagnetic fields in ambient conditions.Boston UniversityPublished versio

Zeptometer metrology using the Casimir effect

In this paper, we discuss using the Casimir force in conjunction with a MEMS parametric amplifier to construct a quantum displacement amplifier. Such a mechanical amplifier converts DC displacements into much larger AC oscillations via the quantum gain of the system which, in some cases, can be a factor of a million or more. This would allow one to build chip scale metrology systems with zeptometer positional resolution. This approach leverages quantum fluctuations to build a device with a sensitivity that can’t be obtained with classical systems.Published versio

Preparation of reduced iron powder for powder metallurgy from magnetite concentrate by direct reduction and wet magnetic separation

The Hoganas method is considered the most effective method for producing reduced iron powder (RIP). How-ever, this method does not remove impurities; therefore, high-purity magnetite must be used as raw materials. In this study, when RIP was produced using magnetite concentrate (TFe = 64.86%), a strong raw material flexi-bility was observed. The influence of various parameters on the preparation of RIP was studied. The results showed that pyrite was the optimal additive, and when used under optimized conditions, it produced RIP with a high iron grade of 99.65%, which meets the standard for powder metallurgy. Analysis revealed that the pyrite additive formed a molten iron sulfide (FeS) phase. Spheroidal metallic iron particles were more easily encapsu-lated by the FeS phase; consequently, the symbiotic relationship between iron and gangue was minimized, which was more conducive to the separation of metallic iron and oxides impurities. Thus, a high-purity RIP was produced. (c) 2021 Published by Elsevier B.V