Nanomechanical resonators using functional nanowires

Nanoelectromechanical systems (NEMS) have seen a surge of active interest in the 21st century. NEMS resonators have been initially employed for mass and force sensing as well as quantum mechanical measurements. With the recent developments in readout techniques at room temperature, NEMS have also proven promising in telecommunications and signal processing applications. Excitingly, NEMS devices operate at the sub-picowatt regime, which is many orders of magnitudes smaller than today’s digital signal processing blocks. Thus, nanomechanical signal processing is becoming an exciting area of research, with the aim of developing effective ways for transducing and tuning mechanical resonances. Currently, active tuning of NEMS is achieved by stress-tuning methods, which rely on the application of net forces to the resonator via electromagnetic fields. However, stress-tuning is volatile, which requires constant electrical stimuli (i.e. quiescent power) to maintain the tuned frequency. Stress-tuning also suffers from reliability issues and alters the quality (Q) factors of the resonators. To overcome these challenges, this thesis investigates a novel technique of tuning nanomechanical resonances by exploiting the Young’s modulus change in chalcogenide-based phase-change materials (PCMs). PCMs can be permanently yet reversibly switched between amorphous and crystalline states, which exhibit different elastic properties. This can be employed as a non-volatile tuning mechanism in NEMS resonators. Recent advances have also shown that nanowire configurations offer a more reliable and homogenous phase transition compared to thin-film PCMs. By using nanosecond-fast electrical pulses for phase-change and employing a piezoresistive readout scheme, the first instance of a non-volatile (power-free) tuning scheme in NEMS has been demonstrated within a range of ~30% using GeTe nanowires. The effect of phase-change on Q factors, phase noise, and piezoresistive gauge factors have also been studied. With non-changing Q factors over 16,000 and a decent phase noise performance, the GeTe nanowires have also been utilised in a frequency-hopping radio transmission. The promises of such a functional resonator are lower power consumption, faster tuning speeds, and better phase noise performance in commercial frequency synthesisers. To improve the signal-to-noise ratio for real-world applications, a novel transduction scheme for nanowires based on cavity optomechanics has further been demonstrated in this thesis, with transduction gain levels of 1.46 mV nm-1 for InP nanowires and 2.02 mV nm-1 for GeTe nanowires at an optical probe power < 75 µW. This thesis also investigates theoretically that these gain levels can be further improved by a factor ~200, extending the field of NEMS beyond academia for the first time, with imminent applications in signal processing and telecommunications. To assemble such a functional platform into a hand-held device, a novel pick-and-place technique has also been developed here, integrating single-crystal nanowires with on-chip devices with a placement precision below 1 µm

Impact of clinicopathological variables on laparoscopic hysterectomy complications, a tertiary center experience

Objectives: To analyze intraoperative and postoperative complications according to Clavian-Dindo Classification (CDC) and evaluate the influence of clinicopathological features on the feasibility and safety of total laparoscopic hysterectomy (TLH) in patients that underwent surgery in a tertiary center. Material and methods: We retrospectively reviewed the database of 469 patients that underwent surgery for patients who underwent extra facial TLH from 2013 to 2020. Results: A total of 86 (18.3%) peri-postoperative complications were observed. The incidence of intraoperative complications was 2% (n = 10). The overall conversion rate to open surgery was 1.9% (n = 9). A total of 76 postoperative complications were observed in 61 patients (14.3%). The incidence of minor (Grade I [n = 16, 3.4%] and II [n = 42, 8.9%]) and major complications (Grade III [n = 15, 3.2%], IV [n = 2, 0.4%] and V [n = 1, 0.2 %]) were 12.3% and 3.8%, respectively. A higher BMI and performing surgery at the first step of learning are found to be associated with intraoperative and postoperative complications (p &lt; 0.05). Postoperative complications related to having a history of the cesarean section, additional comorbidities, and uterine weight ≥ 300 g (p &lt; 0.05). Conclusions: The implementation of TLH by experienced surgeons appears to have remarkable advantages over open surgery. However, the risk factor for complications should be taken into account by surgeons in the learning curve in selecting the appropriate patient for surgery.

A Universal Pick-and-Place Assembly for Nanowires

Funding Information: The authors thank Nathan Youngblood, Benjamin F. Porter, Jia Hao Eugene Soh, and A.Ne for their valuable inputs during discussions. V.K. acknowledges the support of Aalto University Doctoral School, Walter Ahlström Foundation, Elektroniikkainsinöörien Säätiö, Sähköinsinööriliiton Säätiö, Nokia Foundation, Finnish Foundation for Technology Promotion (Tekniikan Edistämissäätiö), Waldemar von Frenckell's foundation and Kansallis‐Osake‐Pankki fund, and the EU H2020‐MSCA‐RISE‐872049 (IPN‐Bio). V.K. and H.L. acknowledge financial support from Academy of Finland Flagship Programme (320167, PREIN) and the technical support by Aalto University at Micronova Nanofabrication Centre. R.A. and G.M. were supported by the ONR‐MURI, grant #N00014‐17‐1‐2661. UEA was supported by The Scientific and Technological Research Council of Turkey (TÜBİTAK) and the Department of Materials, University of Oxford. H.B. acknowledges long‐term support from EPSRC (grants EP/J00541X/2, EP/M015173/1, EP/T023899/1, EP/J018694/1, and EP/R001677/1). Publisher Copyright: © 2022 The Authors. Small published by Wiley-VCH GmbH.With the introduction of techniques to grow highly functional nanowires of exotic materials and demonstrations of their potential in new applications, techniques for depositing nanowires on functional platforms have been an area of active interest. However, difficulties in handling individual nanowires with high accuracy and reliability have so far been a limiting factor in large-scale integration of high-quality nanowires. Here, a technique is demonstrated to transfer single nanowires reliably on virtually any platform, under ambient conditions. Functional nanowires of InP, AlGaAs, and GeTe on various patterned structures such as electrodes, nanophotonic devices, and even ultrathin transmission electron microscopy (TEM) membranes are transferred. It is shown that the versatility of this technique further enables to perform on-chip nano-optomechanical measurements of an InP nanowire for the first time via evanescent field coupling. Thus, this technique facilitates effortless integration of single nanowires into applications that were previously seen as cumbersome or even impractical, spanning a wide range from TEM studies to in situ electrical, optical, and mechanical characterization.Peer reviewe

A universal pick‐and‐place assembly for nanowires (Small 38/2022)

In article number 2201968, Harish Bhaskaran and co-workers develop a universal and deterministic way of assembling single nanowires with a placement precision below 1 micron. They further demonstrate first-of-its-kind devices in the nanowire realm, heralding new opportunities and large-scale nanowire integration

The impact of lesion complexity on no-reflow phenomenon and predictors of reversibility in patients treated with primary percutaneous intervention

Objective