495 research outputs found
Multifrequency atomic force microscopy for the in-plane and out-of-plane nanomechanical characterization of graphitic surfaces
Graphene is considered as one of the most promising materials for numerous applications such as electronics, photonics, membranes, sensors, heat dissipators, lubricants and many more [1, 2]. In addition to its outstanding electronic properties, in particular, the extraordinary mechanical properties of graphene have become the focus of scientific attention. For example, it has been shown that defect-free graphene has an enormously high Young’s modulus of about 1 TPa [3]. However, little research has been done on the local influence of defects on the nanomechanical properties of graphene. Several challenges come to mind as possible reasons, such as (i) imaging graphene with atomic resolution, (ii) simultaneous analysis of sample properties parallel and perpendicular to the sample plane, (iii) preparation of adsorbate-free graphene samples, and (iv) targeted introduction of defects.
To overcome the aforementioned challenges, first, an atomic force microscopy-based method was developed within this work that enables imaging of graphene in air under ambient conditions with atomic resolution. In addition, the method was designed to allow quantification of interaction forces, both, perpendicular and parallel to the graphene surface. This is particularly important to access the complete set of elastic constants of graphene. An important finding of this work is that different adsorbate types could be observed on the graphene surface shortly after the preparation of graphene samples. Therefore, a detailed analysis of the adsorbates was performed using the developed multifrequency atomic force microscopy method. Furthermore, the extent to which oxygen-plasma treatment can be used to remove adsorbates from a graphene sample stored under laboratory air conditions was examined. Adsorbate removal is a basic requirement for the targeted introduction of defects, as well as for the investigation of their influence on the local nanomechanical properties. The effect of oxygen-plasma treatment on different graphene-/graphite-samples was additionally investigated by Raman spectroscopy
Fourier Transform Photoacoustic Spectroscopy with Broadband Lasers
Kaasujen havainnointi on merkittävässä roolissa kestävän, terveellisen ja turvallisen yhteiskunnan luomisessa. Lukuisten eri sovelluskohteiden vaatimukset kaasujen havainnointiin vaihtelevat valtavasti, ja siksi useita erityyppisiä sensoreita tarvitaan. Tämä väitöskirja edistää tätä tavoitetta esittelemällä uuden optisen kaasujen havainnointitekniikan, valoakustisen Fourier-muunnosspektroskopian laajakaistaisella keski-infrapunalaserilla ja herkällä läppämikrofonilla. Tekniikan merkittävimmät hyödyt ovat laajan, ainoastaan valonlähteen rajoittaman spektrisen kaistan nopea mittaus sekä herkkyyden tehokas parantaminen valonlähteen tehoa kasvattamalla. Tässä väitöskirjassa käytettyjen valonlähteiden, superjatkumon ja optisen taajuuskamman hyöty suuren optisen tehotiheyden lisäksi on korkea paikkakoherenssi, joka mahdollistaa erinomaisen spektrisen resoluution sekä tehokkaan kytkennän moniläpäisykammioon.
Tekniikan suorituskyky on erinomainen vaadittavan näytetilavuuden ollessa alle kymmenen millilitraa. Metaanin havaintoraja viiden sekunnin mittausajalla on 90 miljardisosaa, jota voidaan parantaa merkittävästi keskiarvoistamalla. Korkein demonstroitu spektrinen resoluutio on 0.013 cm−1, joka ei heikennä systeemin herkkyyttä ja jota rajoittaa paineleveneminen. Kaksi kertaluokkaa huonompi spektrinen resoluutio kuitenkin mahdollistaa jo hyvän selektiivisyyden monen kaasun samanaikaiseen havainnointiin. Hyvän suorituskyvyn ja pienen näytetilavuuden ainutlaatuisen yhdistelmän ansiosta tekniikka on potentiaalinen esimerkiksi haihtuvien yhdisteiden ja saatavuudeltaan rajoitettujen näytteiden analysoimiseen. Eräs potentiaalinen ja tässä väitöskirjassa demonstroitu sovelluskohde on kemiallisten taisteluaineiden havaitseminen rikostutkinnassa ja jatkuvatoimisissa varoitusjärjestelmissä. Lähitulevaisuudessa sekä tekniikan suorityskyvyn että sovellettavuuden odotetaan kehittyvän merkittävästi, mikä vahvistaa tekniikan asemaa vaihtoehtona teollisiin, lääketieteellisiin ja turvallisuussovelluksiin.Gas sensing plays a key role in the progress towards a healthier, safer and more sustainable society. The amount of gas sensing applications are immense with varying requirements, and thus numerous sensors with different characteristics are needed. This thesis contributes to the task by introducing a new optical gas sensing technique, Fourier transform photoacoustic spectroscopy (FT-PAS) implemented with a spectrally broadband mid-infrared laser and a sensitive cantilever microphone. The main benefits of FT-PAS are the fast acquisition of a wide spectral range that is only limited by the light source, and the effective enhancement of sensitivity with a high-power light source. Two light sources are demonstrated in this thesis, namely an incoherent fiber-based supercontinuum and a frequency down-converted mode-locked optical frequency comb. Besides high power spectral density, the advantage of broadband lasers stems from their high spatial coherence enabling high spectral resolution and efficient coupling to multipass cells.
The performance of cantilever-enhanced FT-PAS is excellent while requiring a sample volume of less than ten milliliters. The detection limit for methane is 90 parts per billion in five seconds, which can be significantly lowered through longer averaging. The highest demonstrated spectral resolution is 0.013 cm−1 with no compromise in the detection sensitivity and limited by pressure broadening. However, two orders of magnitude worse spectral resolution already provides sufficient selectivity for complex multi-species detection. The unique combination of high performance and low gas consumption makes the technique attractive for the analysis of volatile substances and samples with limited availability. The detection of chemical warfare agents for forensic crime scene investigation and online warning systems is one potential application of the technique demonstrated in this thesis. In the near future, both the performance and the applicability of FT-PAS are expected to remarkably improve, establishing the technique as a notable alternative in many industrial, medical and security applications
Spin Detection, Amplification, and Microwave Squeezing with Kinetic Inductance Parametric Amplifiers
Superconducting parametric amplifiers operating at microwave frequencies have become an essential component in circuit quantum electrodynamics experiments. They are used to amplify signals at the single-photon level, while adding only the minimum amount of noise required by quantum mechanics. To achieve gain, energy is transferred from a pump to the signal through a non-linear interaction. A common strategy to enhance this process is to place the non-linearity inside a high quality factor resonator, but so far, quantum limited amplifiers of this type have only been demonstrated from designs that utilize Josephson junctions. Here we demonstrate the Kinetic Inductance Parametric Amplifier (KIPA), a three-wave mixing resonant parametric amplifier that exploits the kinetic inductance intrinsic to thin films of disordered superconductors. We then utilize the KIPA for measurements of 209Bi spin ensembles in Si. First, we show that a KIPA can serve simultaneously as a high quality factor resonator for pulsed electron spin resonance measurements and as a low-noise parametric amplifier. Using this dual-functionality, we enhance the signal to noise ratio of our measurements by more than a factor of seven and ultimately achieve a measurement sensitivity of 2.4 x 10^3 spins. Then we show that pushed to the high-gain limit, KIPAs can serve as a `click'-detector for microwave wave packets by utilizing a hysteretic transition to a self-oscillating state. We calibrate the detector's sensitivity to be 3.7 zJ and then apply it to measurements of electron spin resonance. Finally, we demonstrate the suitability of the KIPA for generating squeezed vacuum states. Using a cryogenic noise source, we first confirm the KIPAs in our experiment to be quantum limited amplifiers. Then, using two KIPAs arranged in series, we make direct measurements of vacuum noise squeezing, where we generate itinerant squeezed states with minimum uncertainty more than 7 dB below the standard quantum limit.
High quality factor resonators have also recently been used to achieve strong coupling between the spins of single electrons in gate-defined quantum dots and microwave photons. We present our efforts to achieve the equivalent goal for the 31P flip-flop qubit. In doing so, we confirm previous predictions that the superconducting material MoRe would produce magnetic field-resilient resonators and demonstrate that it has kinetic inductance equivalent to the popular material NbTiN
The Cryogenic AntiCoincidence detector for Athena X-IFU
Athena is an ESA project for a space telescope for the X-ray astrophysics. The scientific goal is to study the Universe by measuring the evolution of baryonic matter in large-scale structures, such as the warm-hot intergalactic medium, as well as in energetic compact objects. Because most of the baryonic component of the Universe is locked up in hot gas at temperatures of about a million degrees, and because of the extreme energetics of the processes close to the event horizon of black holes, understanding the hot and energetic Universe requires space-based observations in the X-ray band. The topic requires for spatially resolved X-ray spectroscopy and deep wide-field X-ray spectral imaging with capabilities far beyond those of current observatories like XMM-Newton and Chandra.
The observatory will be a fixed 12-meter fixed-focus telescope with two instruments, the innovative X-ray Integral Field Unit (X-IFU), based on cryogenic detectors; and the Wide Field Imager (WFI). These two instruments combine the high spectral resolution of X-IFU with the high spatial resolution of WFI to achieve the scientific goals, with a measurement spectrum from 0.5 to 10 keV.
X-IFU is based on 50 mK cooled Transition Edge Sensors (TES), that exploit the metal-superconductor transition. These can provide the required energy resolution, while offering exceptional efficiency compared to the spectrometers on the current generation of X-ray observatories.
Since the telescope will operate in an environment rich in cosmic rays, it would be impossible to separate the signals from the background on the X-ray detector. In X-IFU, this problem will be solved by an active anticoincidence layer, which would make it possible to achieve the scientific goals for the spectroscopy of faint or distant sources.
The work done in this thesis was focused on the anticoincidence detector, which is one of the core parts of the instrument. Its scope is the reduction of the signal background by about 2 orders of magnitude and will be positioned only 1 mm below the spectrometer. The Demonstration Model (DM) of the detector has been studied, realized and tested. With particular interest in improving the understanding and technology of microfabrication of superconducting devices. The detector is fabricated using optical microlithography and PLD, electro-beam evaporator, and RF-sputtering film deposition systems. The DM active area consists of 96 Ir/Au TES films connected in parallel with superimposed Nb strip lines, insulated with a SiO film, and four heaters on a Si absorber. The pixel is freestanding and attached to a gold frame with four Si beams. The frame is needed to have a strong coupling to a cryostat, since the operating point is below 1 K, and the heaters and the beams are needed to control the decoupling of the active area. Measurements are performed at temperatures around to 0.1 K (the theoretical operating point of X-IFU) in a dilution cryostat reading signals from radiation sources such as Am 241 at 60 keV or Fe 55 at 5 keV. The very low impedance of TES sensors requires a SQuID to read the output signal.
In addition some structural models of the detector have been fabricated and vibrated to understand the structural characteristics and to test the response to stresses that the detector will experience during launch.
Variations of the detector were studied to test its spectroscopic capabilities and to measure its thermal characteristics. To better understand the overall signal generation inside the absorber, a model and simulation of the phononic distribution of the a-thermal transient was developed. Finally, the detector was tested in conjunction with the NASA spectrometer to verify its anticoincidence performance
Applications and Properties of Magnetic Nanoparticles
This Special Issue aimed to cover the new developments in the synthesis and characterization of magnetic nanoconstructs ranging from conventional metal oxide nanoparticles to novel molecule-based or hybrid multifunctional nano-objects. At the same time, the focus was on the potential of these novel magnetic nanoconstructs in several possible applications, e.g. sensing, energy storage, and nanomedicine
Advances in Fiber-Optic Extrinsic Fabry-Perot Interferometric Physical and Mechanical Sensors: A Review
Fabry-Perot Interferometers Have Found a Multitude of Scientific and Industrial Applications Ranging from Gravitational Wave Detection, High-Resolution Spectroscopy, and Optical Filters to Quantum Optomechanics. Integrated with Optical Fiber Waveguide Technology, the Fiber-Optic Fabry-Perot Interferometers Have Emerged as a Unique Candidate for High-Sensitivity Sensing and Have Undergone Tremendous Growth and Advancement in the Past Two Decades with their Successful Applications in an Expansive Range of Fields. the Extrinsic Cavity-Based Devices, I.e., the Fiber-Optic Extrinsic Fabry-Perot Interferometers (EFPIs), Enable Great Flexibility in the Design of the Sensitive Fabry-Perot Cavity Combined with State-Of-The-Art Micromachining and Conventional Mechanical Fabrication, Leading to the Development of a Diverse Array of EFPI Sensors Targeting at Different Physical Quantities. Here, We Summarize the Recent Progress of Fiber-Optic EFPI Sensors, Providing an overview of Different Physical and Mechanical Sensors based on the Fabry-Perot Interferometer Principle, with a Special Focus on Displacement-Related Quantities, Such as Strain, Force, Tilt, Vibration and Acceleration, Pressure, and Acoustic. the Working Principle and Signal Demodulation Methods Are Shown in Brief. Perspectives on Further Advancement of EFPI Sensing Technologies Are Also Discussed
Spektroskopie individuálních molekul v nanokavitě rastrovacího tunelového mikroskopu
Skenovací tunelovou mikroskopií indukovaná luminiscence (STML) v kombinaci s mikroskopií atomárních sil (AFM) s vysokým rozlišením jsou účinným nástrojem pro studium fotofyziky jednotlivých molekulárních chromoforů na čistých površích s atom- ární strukturou. Mechanismus přeměny energie mezi tunelujícími elektrony a vyzářenými fotony v molekulách s nezhybridizovanými stavy nacházejících se v nanokavitě mezi skeno- vací sondou a kovovým vzorkem však není zcela objasněn, neboť závisí na mnoha parame- trech. Tato práce se věnuje rozvoji nových experimentálních přístupů ke studiu těchto sys- témů. Použitelnost hrotů zakončených CO molekulou pro STML jsme ukázali spek- troskopií a prostorovým mapováním intenzity fotonů vyzařovaných zinkovým ftalocya- ninem na substrátu NaCl/kov s rozlišením lepším než nanometr. Ke studiu dynamiky excitonů a náboje v téže molekule v závislosti na přiloženém napětí jsme vyvinuli a ap- likovali metodiku časově rozlišené fázové fluorometrie. Dále jsme studovali vliv prostředí chromoforu na jeho emisní energii a vazebnou energi excitonu. Také jsme u molekul na povrchu jako první pozorovali a objasnili přítomnost molekulárních librací na základě hřebenovitého tvaru emisní čáry, která je výsledkem elektronických přechodů s různými libračními kvantovými čísly a chirální adsorpční...Scanning tunneling microscopy-induced luminescence (STML) combined with high- resolution atomic force microscopy (AFM) is a powerful tool for studying the photophysics of individual molecular emitters on surfaces. However, the mechanism of energy conver- sion between tunneling electrons and photons in decoupled systems placed in a nanocavity of STM is not fully understood as it depends on many variables. This thesis presents a range of proof-of-concept experimental approaches. The vi- ability of CO-terminated tips for STML is demonstrated by performing subnanometer- resolved spectroscopy and mapping of photon intensity acquired over zinc phthalocyanine on NaCl/metal substrate. For the same molecule, time-resolved phase fluorometry is de- vised and is used to reveal the exciton and charge dynamics as a function of the applied bias voltage. Of more fundamental character, the role of the chromophore environment on its exciton emission and binding energy is studied. For the first time, we observed and explained the presence of molecular librations in molecules on the surface from a comb-like emission line resulting from the exciton-libron coupling and the chiral adsorp- tion geometry. Finally, exciton delocalization in molecular aggregates is mapped using the tip nanocavity capable of detecting the dark states,...Matematicko-fyzikální fakultaFaculty of Mathematics and Physic
Synthesis, magnetism and reactivity of graphene nanoribbons
294 p.En esta tesis profundizaremos se enfoca desde un ángulo fundamental la ciencia de las cintas de grafenoPrimero se definirán sus propiedades basándose en ideas bien fundamentadas como la aromaticidad yla topología. Una vez entrados en materia nos centraremos en los 5-armchair y las 3,1-quirales. Se mues-tra un estudio sobre el crecimiento de los primeros que dio lugar al descubrimiento de un nuevo meca-mismo de polimerización. A continuación se estudian sus propiedades para demostrar cómo los 5-aGNR(por sus siglas en inglés) son materiales topológicos que presentan electrones desapareados con actividadMagnética en sus extremos. Este magnetismo está relacionado con una alta reactividad que también se halló en los 3,1-quirales, a pesar de que estos últimos no presentan magnetismo. Se observó una reactividadextrema frente al agua y el oxígeno. La degradación frente a estos elementos generó radicales magnéticoscon capacidad para acoplarse, lo cual presentó una oportunidad de cuantificar y modelizar este acopla-miento en diferentes configuraciones. Por último, se desarrollaron dos estrategias exitosas a la hora deproteger las cintas del ataque ambiental, las cuales pueden ser extrapoladas a otros derivados del grafenoque muestren la recién descubierta reactividad, lo cual facilitaría su transferencia a la industria
Nanomechanical characterization of soft bioelectronic interfaces via modeling-informed atomic force microscopy
The field of bioelectronics involves the use of electrodes to exchange electrical signals with biological systems for diagnostic and therapeutic purposes in biomedical devices and healthcare applications. However, the mechanical compatibility of implantable devices with the human body has been a challenge, particularly with long-term implantation into target organs. Current rigid bioelectronics can trigger inflammatory responses and cause unstable device functions due to the mechanical mismatch with the surrounding soft tissue. Recent advances in flexible and stretchable electronics have shown promise in making bioelectronic interfaces more biocompatible.
To fully achieve this goal, material science and engineering of soft electronic devices must be combined with quantitative characterization and modeling tools to understand the mechanical issues at the interface between electronic technology and biological tissue. Local mechanical characterization is crucial to understand the activation of failure mechanisms and optimizing the devices. Experimental techniques for testing mechanical properties at the nanoscale are emerging, and the Atomic Force Microscope (AFM) is a good candidate for in situ local mechanical characterization of soft bioelectronic interfaces.
In this work, in situ experimental techniques with solely AFM supported by interpretive models for the characterization of planar and three-dimensional devices suitable for in vivo and in vitro biomedical experimentations are reported. The combination of the proposed models and experimental techniques provides access to the local mechanical properties of soft bioelectronic interfaces. The study investigates the nanomechanics of hard thin gold films on soft polymeric substrates (Poly(dimethylsiloxane) PDMS) and 3D inkjet-printed micropillars under different deformation states. The proposed characterization methods provide a rapid and precise determination of mechanical properties, thus giving the possibility to parametrize the microfabrication steps and investigate their impact on the final device
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