This document discusses thin film techniques that could be applicable for superconducting radio frequency (SRF) cavities. It reviews various thin film deposition methods like sputtering, evaporation, and ion beam assisted deposition. Challenges in achieving high quality niobium films for SRF cavities are discussed, including issues like adhesion, purity, defects, grain size, stress. The document provides background on thin film nucleation and growth processes. It also summarizes some previous work done on niobium thin films at the College of William and Mary using DC magnetron sputtering and reactive sputtering.
Anne marie valente feliciano - nucleation of nb films on cu substratesthinfilmsworkshop
In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. All these along with the quality of the Cu substrate have an important influence on the nucleation and subsequent growth of the Nb film, creating a favorable template for growing the final surface exposed to SRF fields. This contribution shows how the structure and defect density thus electron mean free path (represented by residual resistance ratio values) of Nb films can be tailored on Cu substrates, by varying the ion energy and thermal energy provided to the substrate, favoring the hetero-epitaxial or the fiber growth mode.
Anne marie valente feliciano - nucleation of nb films on cu substratesthinfilmsworkshop
In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. All these along with the quality of the Cu substrate have an important influence on the nucleation and subsequent growth of the Nb film, creating a favorable template for growing the final surface exposed to SRF fields. This contribution shows how the structure and defect density thus electron mean free path (represented by residual resistance ratio values) of Nb films can be tailored on Cu substrates, by varying the ion energy and thermal energy provided to the substrate, favoring the hetero-epitaxial or the fiber growth mode.
This to demonstrate the laser ablation of hard materials to form a thin film for optical sensors. The work was done at DIllard University , New Orleans LA by Professor Abdalla Darwish. any comment e-mail adarwish@bellsouth.net.
This is a power point presentation of project work on preparing Zinc oxide thin films by using SILAR technique and CBD technique and studying its characteristics.
3.an update on nano coatings to mitigate corrosion (1)EditorJST
In real time situation machine members are subjected to variable and impact loading experience displacement patterns that may through loading of beam members beyond the yield stress. This causes permanent deformations and excessive fatigue making the beam weak and unserviceable
This to demonstrate the laser ablation of hard materials to form a thin film for optical sensors. The work was done at DIllard University , New Orleans LA by Professor Abdalla Darwish. any comment e-mail adarwish@bellsouth.net.
This is a power point presentation of project work on preparing Zinc oxide thin films by using SILAR technique and CBD technique and studying its characteristics.
3.an update on nano coatings to mitigate corrosion (1)EditorJST
In real time situation machine members are subjected to variable and impact loading experience displacement patterns that may through loading of beam members beyond the yield stress. This causes permanent deformations and excessive fatigue making the beam weak and unserviceable
Chemical Vapour Deposition is a Chemical Synthesis route of Nanomaterials. Specially thin films like Graphene and Carbon NanoTubes are grown by this method.
Influence of Thickness on Electrical and Structural Properties of Zinc Oxide ...paperpublications3
Abstract: Zinc Oxide (ZnO) thin films were prepared on corning (7059) glass substrates at a thickness of 75.5 and 130.5nm by RF sputtering technique. The deposition was carried out at room temperature after which the samples were annealed in open air at 1500C. The electrical and structural properties of these films were studied. The electrical properties of the films were monitored by four-point probe method while the structural properties were studied by X-ray diffraction (XRD). It was found that the electrical resistance of the films decreases with increase in the thickness of the films. The XRD analysis of the films showed that the films have a peak located at 〖34.31^0-34.35〗^0with hkl (002). Other parameters calculated include the stress ( ) and the grain size (D).
In-situ TEM studies of tribo-induced bonding modification in near-frictionles...Deepak Rajput
A presentation on "In-situ TEM studies of tribo-induced bonding modification in near-frictionless carbon films" made by Deepak Rajput. This presentation was based on "critical review of a paper," in All Things Carbon course offered at the University of Tennessee Space Insitute at Tullahoma in Fall 2009.
New technology Model for 1 nm Transistors better than FIN-FET Technology.This slide Tells you in general about the nanotubes, how they are formed and why they are better than MOSFETs
There is no dubt that the subject of superconducting resonant cavities is a fascinating field both physical and engineering point of view.
The application of superconductivity to the world of resonant cavities has made achievable results unimaginable otherwise.
Independently of the special field of application, superconducting resonant circuits have superior performances compared to roo-temperatire circuits.
However the greatest resource of such devices stays not in the high quality of the results already obtained, but in all potential applications and new ideas that must be still developed.
When hearing about persistent currents recirculating for several year in a superconducting loop without any appreciable decay, we realize that we are dealing with a phenomenon wich in nature is the closest we know to the perpetual motion.
The zero resistivity and the perfect diamagnetism in Mercury at 4.2 K, the discovery of superconducting materials, finally the revolution of the "liquid Nitrogen superconductivity": Nature discloses drop by drop its intimate secrets.
Nobody can exclude that the final surpreise must still come.
This works deals with the A15 compound synthesis on niobium samples and over the
internal surface of niobium cavities by means of induction heating. Specifically, three compounds were studied: Nb3Ga, Nb3Al and Nb-Al-Ga. As for the preparation of the niobium samples, they were treated with BCP solution in order to polish the surface. The niobium cavities were treated with centrifugal tumbling, BCP solution and high pressure water rising. Subsequent, the samples, or cavities, were placed into an inductor controlling the voltage, time, sample position, temperature, type and pressure of gas used. The highest critical temperature
obtained was 18 K and Tc 0,35 K, in Nb-Al-Ga#1 sample by inductive measurement.
Mapping analysis showed the uniform diffusion of aluminum into the niobium, and the gallium diffuses creating channels into niobium. The composition was measured by EDS obtaining (82±1)% wt. Niobium, (11,3±0,9)% wt. Gallium, (4,7±0,2)% wt. Aluminum and (1,9±0,1)% wt. Oxygen. Finally, RF test confirmed that the cavities obtained after the annealing were normal conductive indicating that the preparation parameters must still be optimized.
In questi ultimi anni i problemi energetici e ambientali hanno favorito lo sviluppo di un nuovo settore della ricerca riguardo la produzione di energia pulita sfruttando fenomeni naturali. L'attenzione dei ricercatori è stata catturata dalla possibilità di convertire l'energia solare luminosa
in energia elettrica. Questo processo di conversione, nato nella prima metà del XX secolo, permette di produrre correnti elettriche anche in piccola scala, senza la realizzazione di imponenti impianti industriali e soprattutto senza la produzione si scorie inquinanti. Sono nate così le prime celle solari
a effetto fotovoltaico.
Gli sviluppi hanno portato a diversi risultati e al giorno d'oggi l'energia fotovoltaica ha ormai fatto il suo ingresso nella vita quotidiana. Sia i favori delle industrie, sia l'interesse dei privati cittadini, contribuiscono a espandere questo tipo di ricerca, ottenendo numerosi successi nell'aumento
dell'efficienza di conversione energetica. Dal punto di vista della scienza dei materiali la prima cosa che viene in mente pensando alle celle
fotovoltaiche è il silicio. A tutti gli effetti la maggior parte delle celle sul commercio sono costituite da silicio policristallino, per le sue ottime qualità e proprietà di resa. Tuttavia esistono anche una moltitudine di altri composti, alcuni più recenti di altri, che sono ancora nell'occhio dei ricercatori, un esempio ne sono i recenti foto-materiali organici. Spesso però i costi di realizzazione sono alti per ottenere rese elevate, rendendo così proibitive le realizzazioni su impianti industriali. L'ossido rameoso (Cu2O) è stato uno dei capostipiti dei materiali utilizzati nelle celle fotovoltaiche.
Fin dal suo primo utilizzo nel 1958 esso ha presentato le caratteristiche di semiconduttore necessarie alla realizzazione di impianti fotovoltaici. Rispetto ai sui cugini più nobili, presenta delle efficienze minori, ma anche un costo decisamente più basso. Il rame infatti, da innumerevoli anni, è un elemento largamente sfruttato in tutti i campi dell'elettronica e non solo, e la realizzazione di ossidi specifici non comporta processi troppo complessi o costosi.
La ricerca nel campo dell'ossido rameoso è riuscita a migliorare le sue qualità all'interno del mondo fotovoltaico rendendo possibile la realizzazione di celle solari a costi contenuti.
Per questo motivo il Cu2O è tutt'oggi un materiale in grado di competere nel moderno panorama della ricerca solare fotovoltaica.
Il plasma è un supporto particolarmente attivo dal punto di vista chimico e fisico. In base al modo con cui viene attivato e alla potenza di lavoro, può generare temperature basse o molto elevate e viene definito rispettivamente come plasma freddo o caldo. Quest’ampio range di temperature lo rende adatto a numerose applicazioni tecnologiche: rivestimento di superficie, smaltimento rifiuti, trattamento dei gas, sintesi chimiche, lavorazioni industriali. La maggior parte di queste applicazioni del plasma non sono ancora state industrializzate, sebbene il loro sfruttamento rispetti strettamente le norme sull’inquinamento.
I plasmi caldi (specialmente quelli ad arco) sono ampiamente industrializzati, con particolare diffusione all’interno del settore aereonautico. La tecnologia dei plasmi freddi è stata sviluppata in microelettronica, ma le apparecchiature da vuoto richieste ne limitano l’applicabilità.
Al fine di evitare l’inconveniente associato al vuoto, molti laboratori hanno provato a trasferire a pressione atmosferica processi che attualmente lavorano in vuoto. Le ricerche condotte hanno portato alla scoperta di varie ed innovative sorgenti che verranno descritte in questo elaborato.
Dopo un riassunto sui differenti tipi di plasmi, saranno descritte le varie sorgenti in termini di design, condizioni di lavoro e proprietà del plasma. In seguito l’attenzione sarà spostata sulle varie applicazioni (analisi spettroscopica, trattamento dei gas e processi sui materiali).
The lowest possible surface resistivity and higher accelerating field are the paramount
considerations, hence are obligatory for accelerating cavities. Since, superconducting materials
are used to make radio-frequency cavities for future accelerators. In the case of rf cavities,
superconductors are being used in order to minimize the power dissipated and increase the
figures of merit of a radio-frequency cavity, such as the quality factor and accelerating gradient.
Hence, these could be achieved by improving surface treatment to the cavity, and processing
techniques must be analyzed in order to optimize these figures of merit.
The research work reported in this dissertation mainly carried out on tesla type seamless 6GHz
Nb and Cu cavities. We have developed two innovative techniques: firstly, for mechanical
polishing of cavities, and secondly for purification of these cavities at atmospheric pressure under
cover of 4Helium gas (for protection) and at ultra-high vacuum (UHV) system. These cavities are
fabricated by spinning technology to create seamless cavities.
The main advantages of 6 GHz bulk-Nb cavities are saving cost, materials and time to collect
statistics of surface treatments and RF test in a very short time scale. Cavities are RF tested
before and after high temperature treatment under atmospheric pressure (under cover of inert gas
atmosphere to protect inner and outer surface of cavity) inside transparent quartz tube, and under
UHV conditions. Induction heating method is used to anneal the cavity at temperatures higher
than 2000°C and close to the melting point of Nb for less than a minute while few seconds at
maximum temperature. Before RF test and UHV annealing, the surface treatment processes like
tumbling, chemical, electro-chemical (such as BCP and EP), ultrasonic cleaning and high
pressure rinsing (HPR) have been employed. High temperature treatment for few minutes at
atmospheric pressure allow to reduce hydrogen, oxygen and other elemental impurities, which
effects on cavity Q-factor degradation, hence recovers rf performances of these cavities. This
research work will address these problems and illustrate the importance of surface treatments.
6 GHz spun seamless Superconducting Radio Frequency (SRF) cavities are a very
useful tool for testing alternative surface treatments in the fabrication of TESLA cavity.
However, the spinning technique has also some drawbacks like contamination, surface
damage in internal part due to the collapsible mandrel line. The first important step of
the surface treatments is the mechanical polishing. For this purpose, a new, cheap, easy
and highly efficient tumbling approach based on vibration was developed.
Before this approach was conceived, a few other methods, such as Turbula,
Centrifugal Barrel Polishing (CBP), custom Zigzag tumbler and “flower brush” have
been studied and tested. But the result was not so satisfactory neither for the low erosion
rate nor for the unstableness of the system nor for the complicated polishing process. At
last, a vibration system with a simple structure, working stably was created after two
experiments.
Another important task of the thesis is to update the optical inspection system for 6
GHz cavities. 3 stepper motors motor was added to move and rotate the cavity and
realized auto focus of the miniature camera. A software was developed to achieve a full
cavity photographed by one key operation using LabVIEW.
A high-efficiency mechanical polishing system is generally judged by two aspects:
one is whether the surface property satisfies the demand after polishing; the other is
whether the erosion rate can reach and be stabilized at a high value which is comparable
or greater than the existing products. The Radio Frequency (RF) test result indicates that
the vibration system is feasible. The latest erosion rate 1 gram/hour i.e. removing 13
microns depth of inner surface materials per hour exceeds the performance of CBP,
which is widely used in other laboratories in the world.
The mechanical polishing process is elaborated and cavities that have been polished
are listed. Several influencing factors on the erosion rate, such as tumbling time, media,
signal and multi-cavities and plate direction are discussed at the end.
A preliminary design of 1.3 GHz vibration system as the future development is
provided for the next plan.
In questo lavoro di tesi verrà presentato un primo prototipo di un mini inceneritore al plasma per la pirolisi dei rifiuti medicali basato sulla tecnologia delle torce al plasma a microonde (MW) con tecnologia domestica a basso costo.
Si inizia con una breve e generale descrizione sulle problematiche dei rifiuti, della loro classificazione e delle norme che ne regolano lo smaltimento. Quindi si parlerà delle norme necessarie per l‟identificazione dei rifiuti medicali ed infine verrà riassunta la modalità di gestione dei rifiuti secondo la normativa in vigore.
Successivamente saranno descritti alcuni metodi di termodistruzione dei rifiuti ospedalieri come la combustione negli inceneritori tradizionali, e alcuni metodi alternativi, come il trattamento al plasma atmosferico, andando ad analizzare vantaggi e svantaggi di ogni tecnologia.
L‟attenzione sarà quindi focalizzata sul plasma atmosferico e sulla descrizione delle sue proprietà. Quindi saranno descritti diversi tipi di plasma atmosferico in base alle condizioni operative di alimentazione e delle loro strutture concentrando le nostre attenzioni verso le torce al plasma atmosferico basate sulle microonde.
Quindi si descriverà la realizzazione di una torcia al plasma atmosferico utilizzando i componenti a basso costo dei normali forni a microonde e con l‟obbiettivo di utilizzare questa torcia sia nel settore industriale che nella ricerca.
Tale torcia, realizzata con componenti commerciali domestici a basso costo, costituirà il cuore del prototipo di mini inceneritore che è stato progettato, realizzato, descritto e testato in laboratorio. Verrà quindi illustrata l‟efficacia di trattamento di materiale rappresentativo di rifiuti medicali come: carta, cotone idrofilo e tessuti organici biologici.
Infine verranno descritte le linee guida per gli sviluppi futuri del prototipo al fine di aumentarne l‟efficienza nel trattamento dei rifiuti, nel recupero dell‟energia derivante dalla combustione dei syn-gas e nella purificazione dei gas da agenti inquinanti.
The subject of present Master Work is the thermomechanical design of a high power neutron converter for the SPIRAL2 Facility, which is being developed in collaboration with the INFN – Italy and GANIL – France.
The main objective is description of an general overview about the project and its main goals. The SPIRAL2 is a linear particle accelerator for the production of high intensity exotic ion beams. It will be under operation in the existing installations of the GANIL Institute in Caen, France. Therefore a neutron converter target has been designed and it must produce 1014 fissions/second, at a working temperature up to 1850°C. Available deuteron beam for the operation of this accelerator has a power up to 200 kW and all the calculations and tests around the main critical elements of the neutron converter module are explained in the next sections of this document.
Superconducting technique has been widely applied to linac particle accelerators for more than two decades. Cryogenic RF performance of SC cavities has been improved a lot due to improvement on purification of SC material, as well as SC cavity design, fabrication and surface treatment techniques. The Sputtering technique of SC cavities provided another chance to particle accelerators: the cost of cavity fabrication greatly decreased, while the performances of sputtering coated niobium cavities are competitive with those of bulk material SC cavities.
In this thesis some important features of RF cavities are briefly introduced; the difference in design of a SC cavity and that of a normal conducting cavity are indicated. The design parameters of a 144 MHz SC QWR and an 1.5GHz monocell spherical cavity are presented. The SC material for cavity fabrication, and measurement method of SC cavity are introduced, then the fabrication and surface treatment technique of SC cavities are discussed.
The application of sputtering technique in SC cavities is a recent development of SRF technique. After nearly two decades study, the sputtering coated niobium film SC cavities achieved a cryogenic RF performance close to that of bulk niobium cavities. The thesis introduced various sputtering techniques on this purpose from preliminary glow discharge, discusses the LNL, Peking University and Australia National University’s QWR sputtering configurations, and introduces LNL’s surface treatment technique for copper substrate cavity.
In the study of niobium sputtering for 1.5GHz monocell spherical cavity, different magnetron configurations were tried and measured a large amount of sputtered niobium samples. By improving the magnetron configuration and surface treatment technique of the substrate cavity, sputtered niobium cavities with better RF performance were obtained. It was found out that substrate surface treatment takes a very important role in the sputtering of a SC cavity, as sample measurement cannot give out helpful information of the RF performance, the study with substrate
Il forno in alto vuoto della TAV è stato costruito per l’Istituto Nazionale di Fisica Nucleare agli inizi degli anni novanta ed è installato presso i Laboratori Nazionali di Legnaro (PD) nello stabilimento Alte Energie.
E’ stato realizzato in collaborazione con la ditta milanese TAV, che ha sede a Caravaggio (MI), specializzata nella produzione di forni in vuoto. E’ stato così possibile realizzare un forno mai costruito prima e che rispondeva appieno alle esigenze richieste.
Il forno in vuoto allora in uso era un modello a caricamento orizzontale le cui pareti interne e le resistenze erano realizzate in grafite. Da allora il vecchio forno è stato congedato, mentre il nuovo impianto è entrato subito in funzione per eseguire le brasature e i trattamenti termici sulle cavità acceleratici superconduttive a quarto d’onda dell’impianto Alpi.
Da allora fino ad oggi, il nuovo forno è sempre stato operativo, e grazie ad esso è stato possibile realizzare una grande varietà di trattamenti termici e brasature, per le più svariate applicazioni e impieghi.
La tecnologia degli acceleratori di particelle è tradizionalmente un serbatoio da cui attingere per il trasferimento di conoscenze tecniche dall’ambito della ricerca di base all’industria; in questo campo i Laboratori Nazionali de Legnaro dell’Istituto Nazionale di Fisica Nucleare (LNL – INFN) vantano una lunga esperienza come ente di ricerca di alto livello sia in ambito italiano che internazionale, nello sviluppo di nuove tecniche di accelerazione e nell’applicazione di conoscenze e metodologie tipiche della scienza dei materiali al campo degli acceleratori di particelle. Il master in Trattamenti di superficie applicati a tecnologie meccaniche innovative per l’industria si inserisce in questo contesto e funge da ponte per il trasferimento del bagaglio di conoscenze maturate durante gli anni per il trattamento dei materiali delle cavità acceleratrici a realtà industriali presenti sul territorio nazionale.
Il trattamento superficiale di una cavità acceleratrice superconduttiva è un passaggio fondamentale nella sua realizzazione, in quanto predispone lo strato superficiale del risonatore stesso a sostenere le condizioni di vuoto, temperatura ed alti campi elettrici presenti durante il funzionamento nell’acceleratore; questi trattamenti presuppongono un’approfondita conoscenza della scienza dei materiali ed una robusta preparazione di tipo applicativo oltre che teorico.
Il lavoro di questa tesi prende l’avvio da due istanze fondamentali, cioè
dall’applicazione delle conoscenze fisiche, chimiche e meccaniche apprese nel corso del master e dalla tradizione nello sviluppo di nuove tecniche di accelerazione dei Laboratori Nazionali di Legnaro con il fine di realizzare e caratterizzare un nuovo tipo di strutture acceleranti basate sul concetto di cristallo fotonico o photonic band gap (PBG) applicato alle microonde.
Durante questo lavoro si sono quindi realizzati alcuni prototipi di cavità PBG risuonanti a 14 e 6 GHz, in rame ed in niobio superconduttivo, sviluppando un metodo realizzativo che permettesse di evitare il ricorso a costose saldature electron beam; le cavità così realizzate sono state trattate superficialmente adattando il protocollo di trattamento utilizzato per altre cavità costruite nei Laboratori e studiando nuove strade tecniche per la loro finitura superficiale. Infine si è proceduto ad adattare i sistemi criogenici e RF
integrandoli per caratterizzare le cavità costruite.Questo progetto si inserisce in una collaborazione fra i Laboratori Nazionali di Legnaro
e la sezione INFN di Napoli, che ha fornito il supporto teorico sulla teoria dei cristalli fotonici applicati agli acceleratori e ha contribuito al progetto delle cavità attraverso le simulazioni dei campi elettromagnetici in cavità; il gruppo di legnaro si è occupato, oltre che della costruzione, dei trattamenti di superficie e delle misure, anche della parte riguardante la superconduttività in Radiofrequenza.
L’obiettivo di questo lavoro consiste nella progettazione e costruzione di un sistema UHV multicamera per la deposizione di film sottili. La tecnica
utilizzata per crescere i ricoprimenti sottili in questo caso è l’arco catodico continuo e pulsato. Questa tecnica permette di depositare film di elevato spessore in tempi estremamente veloci. La sorgente è pressoché puntiforme in confronto allo sputtering ed i film possono essere più spessi e più puri.
L’arc vapour deposition è una tecnica di deposizione di film sottiliche cade nella grande famiglia del PVD. Essa consiste nella vaporizzazione, da un elettrodo, del materiale che si vuole depositare per mezzo di un arco. La tecnica è veloce, efficiente e relativamente poco costosa: di conseguenza è uno dei metodi più usati a livello industriale per ottenere deposizioni di film sottili con ottime proprietà meccaniche.
Negli ultimi anni si stanno effettuando numerose ricerche, sia sperimentali sia
teoriche, al fine di mettere in evidenza come questa tecnica possa essere molto utile per produrre dei film sottili in grado di aumentare le proprietà fisiche e chimiche dei rivestimenti (come ad esempio un aumento della densità, un miglioramento dell’adesione al substrato, della stechiometria dei composti e di ulteriori caratteristiche chimico-fisiche).
In particolare la letteratura russa tratta numerosi esempi di come la tecnica
dell’arco, proprio grazie all’alto grado di ionizzazione dei vapori prodotti, renda possibile la produzione di rivestimenti con determinate proprietà chimico-fisiche e strutturali per particolari condizioni di processo, non altrimenti ottenibili con altre tecniche competitive quali il magnetron sputtering o l’evaporazione tramite electron beam Come si vedrà in
seguito, infatti, l’arc vapour deposition ha il grandissimo vantaggio di controllare non solo la ionizzazione degli atomi che si vogliono depositare, attraverso una combinazione di campi elettrici e magnetici, ma anche l’energia con la quale gli ioni arrivano sul substrato.
Le sorgenti ad arco vengono inoltre utilizzate come sorgenti per LRQ EHDP che
devono produrre elevate densità di corrente.
Nel mondo industriale, infatti, questa tecnica riscuote molto interesse.Il deposito tramite arco catodico è un processo fisico sottovuoto che consente la
crescita di film duri, compatti ed aderenti su un ampio spettro di materiali al di sotto dei 300°C: Il film, estremamente sottile, ha durezze da 1000 a 3500 HV: le applicazioni industriali sono molte e variano dalla ricopertura di utensili da taglio agli tampi per le materie plastiche e lavorazioni meccaniche, da prodotti d’arredamento (maniglie, copri interruttori, pomoli, etc.) a componentistica da bagno (rubinetti, docce, tubi, etc.).
......
Fu una scoperta sensazionale quando Jun Akimitsu e colleghi annunciarono la loro scoperta nel gennaio 2001 che il diboruro di magnesio diveniva superconduttore attorno ai 40 K. L’interesse degli autori era inizialmente rivolto verso il semiconduttore CaB6 , il quale diviene ferromagnetico a seguito di trattamento leggero di doping. La loro intenzione era quella di sostituire parzialmente degli atomi di carbonio con altri di magnesio, omologo come shells elettronici ma più leggero, e gli parve conveniente utilizzare il diboruro di magnesio (ben noto sin dal 1953) per questo scopo.
L’aspetto interessante è che il magnesio diboruro è un composto molto usato nelle reazioni di sintesi del boro, dei borani, o di bururi di metalli di transizione e facilmente reperibile in qualsiasi laboratorio di chimica. E’ dunque facile immaginarsi lo stupore del mondo scientifico quando fu
comunicato che il MgB2 diviene superconduttore a temperature mai raggiunte sino ad allora da sistemi basati su semplici leghe intermetalliche non ossidate. Le fievoli speranze ed il derivante
mitigato interesse che vi era attorno ai superconduttori all’inizio della seconda metà del 1900 era dovuto soprattutto a due figure ....
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Rosa alejandra lukaszew a review of the thin film techniques potentially applicable to cavities
1. A review of the thin film techniques
potentially applicable to cavities
Rosa A. Lukaszew, B. Burton, M. Beebe, William M. Roach,
College of William and Mary, Williamsburg, Virginia, USA
C. Clavero, LBNL
Grigory V. Eremeev, Charles E. Reece, Anne-Marie Valente-Feliciano, L. Phillips
Thomas Jefferson National Accelerator Facility [TJNAF], Newport News, Virginia,
USA
2. Why thin films?
In the 2012 workshop at Jlab L. Phillips pointed out:
• Cost is the main driver
– Thin film niobium cavity substrates are of castable metals, such as
copper or aluminum.
– Enables integration of many system functions in a single low-cost
structure, i.e. an aluminum casting.
– Integrated functions
– Cavity RF surface definition
– High thermal conductivity substrate
– Helium vessel
– Cryogenic manifold with heat exchanger
– Cavity stiffening, and many more……….
• Future applications of SRF linacs for which cost is a driver: ILC, or
LEP3, ADS, medical, light sources, ….
3. The Challenge of Nb-coated SRF Cavities:
Coatings have the promise of very substantial savings
• bulk Nb cavities are very expensive
• the gradient challenge: higher gradient
implies less cavities, significant savings
• potentially even greater savings with
cavities with Nb films
• so far mixed results for sputtered films
– adhesion issues
– low RRR
– Q-slope at high field
– breakdown even at relatively low field
typical bulk Nb cavities
best sputtered Nb films
on electropolished Cu
cavities (Benvenuti)
(Padamsee)
Fig. 4 of C. Benvenuti et al., Physica C:
Superconductivity 351, 421 (2001).
Nb films on copper are considered a proven
technology for up to about 10 MV/m
LEP (1996): 216 cavities with sputtered Nb,
6 MV/m with Q0 = 3.4 x 109 at 4.5 K
the quality factor Q0 of magnetron-sputtered
cavities slopes down with
increasing RF electric field
4. Other advantages
• The micro-structure and contaminant levels of the RF
surface can –in principle- be controlled.
• Stable diffusion barriers can be added in situ impeding the
development of oxides or other forms of atmospheric
degradation after exposure to air.
• Other materials can be considered.
But:
• Practical issues that need attention:
– Control of film thickness over complex shapes
– Materials of relevance are compounds and techniques for
coating the interior of cavities while maintaining stoichiometry
and SRF proper ties within restricted limits of film thickness also
requires control.
5. Some History of thin films for SRF
cavities
• Since SRF is a surface phenomenon where only ~10
penetration depths are needed (=40 nm for niobium),
it was recognized for some time now that it would be
economically convenient to use thin film coated
cavities.
• Earlier attempts at CERN applied standard sputter PVD
methods, but the grain size for the CERN Nb/Cu films
was 100 nm, which is 10,000 times smaller than for
conventional SRF cavities with the ensuing problems
that appear at grain boundaries.
• Thus, these prior attempts showed higher surface
resistance and worst Q-slope than bulk.
6. Previous reviews
• A 2006* review by Sergio Calatroni of CERN discusses some
of the problems:
– Defects within 1 or 2 of the surface or on the surface.
Insufficient attention has been paid to this topic, including
trapping of impurities like oxygen in defects.
– The grain size for the CERN Nb/Cu films is 100 nm. This is 10,000
times smaller than for conventional SRF cavities, (for which grain
sizes are > 1 mm and are not important).Grain boundaries are
themselves one-dimensional defects. Grain boundary diffusion
is much faster than diffusion in the bulk Nb.
– Local thermal conductivity of the film itself may be poor
compared to bulk Nb.
– Interfacial thermal resistance, also known as thermal boundary
resistance, or Kapitza resistance at two interfaces: Nb/Cu and
Cu/LHe(II)
* Physica C: Superconductivity, Volume 441, Issues 1–2, 15 July 2006, 95–101
7. Coating Nb on SRF Cavities is promising but challenging
• Electroplating: not clean enough
• atomic layer deposition: promising but slow
• sputtering in UHV: low RRR, low Q
• filtered cathodic arc in UHV: tricky particle and geometry issues
• emerging: sputtering technology with ionization
Film issues include
adhesion
purity
defects (like substrate defects and
particulates)
grain size and texture
stress (intrinsic and thermal)
thermal conductivity of base material
at cryogenic temperature can be better
than bulk niobium (copper!)
affecting SRF performance
8. Classify thin films
• Crystalline
– atoms show short and
long range order
• Polycrystalline
• Amorphous
– atoms show short range
order only
– Glasses; not stable state
for most pure metals;
generally less dense than
crystalline materials.
• Typical defects:
– grain boundaries
– Dislocations
– Point defects
– Surface roughness
9. Can we understand TF nucleation?
• Nucleation from a liquid phase to a solid depends on:
– Liquid phase instability (going through a phase change
from higher to lower T)
– Diffusion of atoms into clusters (increases with T)
10. Film formation
• Competing Processes
• adding to film:
– impingement
(deposition) on surface
• removing from film:
– reflection of impinging
atoms
– desorption (evaporation)
from surface
• Steps in film formation:
1. thermal
accommodation
2. binding
3. surface diffusion
4. nucleation
5. island growth
6. coalescence
7. continued growth
12. From kinetic theory of gases
• How many gas
molecules collide with a
surface each second ?
• How long does it take to
form a complete layer
of gas on a surface?
pressure tm
1 atm 2 x 10-9 sec
10-6 torr 2 seconds
10-9 torr 31 minutes
13. Contamination
• PROBLEM: residual gas
in chamber gives two
"sources" impinging
• evaporant:
• residual gas:
Impurity concentration
SOLUTION:
• better vacuum
• higher deposition rate
14. Sputter deposition
• target atoms and ions impinge
• electrons impinge
• Ar atoms impinge
– Ar pressure about 0.1 torr
• Ar may be incorporated into film
• energetic particles may modify
growth
• substrates heat up
15. Variations
• Ion assisted deposition (IBAD)
– with evaporation or sputtering (or
chemical vapor deposition)
• bombard surface with ions
– not necessarily same type as in film
• ions typically NOT incorporated in
film
• relatively low voltages (50 - 300 eV)
• leads to
– physical rearrangement
– local heating
• can change film properties
– for better or worse
• disruption of columnar (fiber) growth
requires about 20 eV of added
energy per depositing atom
• Reactive Sputter deposition
• add reactive gas to chamber during
deposition (evaporation or
sputtering)
– oxygen, nitrogen
• chemical reaction takes place on
substrate and target
• can poison target if chemical
reactions are faster than sputter rate
• adjust reactive gas flow to get good
stoichiometry without incorporating
excess gas into film.
16. Arc
• high current, low voltage
discharge initiate by
touching electrode surfaces
and then separating trigger
arc by high voltage
breakdown
• produces large numbers of
electrons
• very efficient ionization of
film atoms (almost 100 %)
• impinging ions may be high
energy
– enhanced chemical reactions
– film densification
17. Plasma sources
• plate electrodes
– low plasma densities (109 - 1010
charged particles per cm3)
– common in sputter deposition
• Inductively coupled plasma
(ICP)
– high plasma densities (1011 -
1012 charged particles per cm3)
– operates well at lower gas
densities (< 50 mTorr)
– can be used up to atmospheric
pressures (and beyond)
– couple RF energy inductively
into plasma (lossy electrical
conductor)
– produces more efficient
ionization
• Electron cyclotron resonance
(ECR)
– high plasma densities (1012 -
1013 charged particles per cm3)
– operates well at lower gas
densities (down to 0.1 mTorr)
– couples microwave energy to
electrons by matching
frequency to electron gyration
frequency
– produces more efficient
ionization
– control the plasma density with
microwave power and gas
pressure
– can also control ion species
created.
18. A note on metallic thin films
• The properties of thin films
depend on their
microstructure.
• The stability of thin metal films
depends on being deposited
on appropriate substrates.
• Important characteristics are
residual stress and strain,
which often develop in film-substrate
combinations An
unfavorable consequence of
high stress is crack formation,
local plastic deformation, and
layer delamination.
• Residual stresses, which are
commonly assumed to be
biaxial in thin films, result from
different thermal expansion
coefficients of substrate and
film (thermal stress) and/or
from stress formation during
film deposition (grown-in
stress)
• In polycrystalline films a
central mechanism that
governs stress relaxation by
inelastic deformation is
thought to be atomic
diffusion, predominantly along
grain boundaries.
19. Examples
• Quantitative, quasisimultaneous in situ
characterizations of the modification of
vacancy concentration and of residual
strain in metallic films have been carried
out for particular cases (e.g Pt thin films,
PRL 107, 265501, 2011).
• This work was based on based on x-ray
scattering techniques. This has the
advantage that the use of synchrotron
radiation becomes possible, which
allowed to carry out time-resolved
studies to measure fast relaxation
processes taking place on a time scale of
minutes.
• In order to detect directly the
modification of the vacancy
concentration, x-ray diffractometry (XRD)
was used to determine the of the out-of-plane
lattice parameter a and x-ray
reflectivity (XRR) was used to detect the
film thickness.
20. SRF Thin film coating approaches
• CVD (L. N. Hand, Cornell, USA) and ALD (T.
Proslier, ANL) have been explored.
• A hybrid physical-chemical vapor deposition
(HPCVD) technique at Temple University has
resulted in optimal MgB2 films.
• Energetic PVD processes such as ECR (A.-M.
Valente-Feliciano, Jlab; private companies),
HiPIMS (A. Anders, LBNL) vacuum-arc (R. Russo)
have also been reported as suitable techniques
for this application.
21. Opportunities for energetic PVD Niobium Films
• Two major limitations of conventional magnetron
sputtering are:
– Low deposition energy of arriving atoms limiting control of film
structure
– Presence of argon gas being incorporated into the growing film
in addition to spatial limitations of the plasma
• Both issues are eliminated by using niobium ions in vacuum
to deposit films.
– Control of film microstructure through energetic condensation
– High adatom surface mobility
– Sub-plantation
– Grain competition driven by incident ion energy selective
sputtering, channeling, surface energy of crystal face
22. Energetic Condensation
• Energetic condensation is a deposition process where a significant fraction of the condensate
has hyper‐thermal energies (energies 10 eV ). A number of surface and subsurface
processes are activated or enabled by the energy of the particles arriving at the surface (e.g.
desorption of adsorbed molecules, enhanced mobility of surface atoms, and the stopping of
arriving ions under the surface). The purpose of using energetic condensation deposition
methods is to improve film structure while keeping the substrates at lower temperature by
adding energy to the film during condensation to compensate for lack of thermally induced
growth processes.
• For example crystalline defects, grains connectivity and grain size may be improved with a
higher substrate temperature that provides higher surface mobility. However the substrate
used may not allow substantial heating and in such case the missing energy may be supplied
by ion bombardment. In bias sputter deposition a third electron accelerates the sputtering
gas ions, removing the most loosely bound atoms from the coating, while providing
additional energy for higher surface mobility
• One possible process, ion beam assisted deposition (IBAD), uses a secondary source of ions
to co‐bombard the film from conventional sources during growth.
• A second process, direct ion deposition, uses vacuum plasmas formed from the material
being deposited to produce a film grown from metal ions.
23. Approach:
Use a plasma-based technology for “Energetic Condensation”
A. Anders, Thin Solid Films 518 (2010) 4087
Generalized Structure zone Diagram (2010),
derived from Thornton’s diagram for
sputtering (1974)
24. High Power Impulse Magnetron Sputtering
( a form of IBAD)
Copper target
2” magnetron
A. Anders(LBNL)
25. Illustration of Self-sputtering
target
Self-sputtering runaway
1
substrate
ions to substrate atoms to substrate
Sustained self-sputtering
1
Probability
for ions
to return to
the target
Ionization
probability
yield
adapted from: A. Anders, J. Vac. Sci. Technol. A 28 (2010) 783
26. Our work using DC magnetron sputtering
and reactive sputtering at W&M
• We have investigated the
effect of microstructure and
morphology on the
superconducting properties
of Nb thin films deposited
onto different ceramic
surfaces and metallic
surfaces.
• In particular we studied a-plane
sapphire and (001)
MgO and Cu (001).
• We monitored the
microstructure of the films,
the morphology of the
surface and the
superconducting properties
as well as the DC properties.
• We explored several aspects
in the thin film deposition
parameters-space, such as
growth rate, substrate
temperature during growth,
annealing treatments, etc.
27.
28. Nb growth on a-plane sapphire
• Nb can grow epitaxially on a-plane sapphire, with Nb(110)//Al2O3(11-20)
Comparison of RRR values obtained by different groups:
Group Nb film thickness
(nm)
RRR
Lukaszew 600 97
S. A. Wolf [1] 600 82
G. Wu [2] 235 50.2*
* RRR values for niobium thin films is highly dependent on thickness
[1]. S. A. Wolf et al., J. Vac. Sci. Tecnol. A 4 (3), May/June 1986
[2] G. Wu et al., Thin Solid Films, 489 (2005) 56-62
29. Early stages of growth
Nb thickness (nm)
[111]Nb ll[0001]Al O 2 3
bulk Nb bcc
hcp Nb
[1120]Nb ll
[0001]Al O 2 3
1 10 100
0.36
0.35
0.34
0.33
0.32
0.31
0.30
0.29
0.23 2.3 23
Lattice parameter (nm)
Nb atomic layers
a
bcc Nb
hcp+bcc Nb
a
• Using Reflection high energy
electron diffraction (RHEED), we
observed a hexagonal Nb
surface structure for the first 3
atomic layers followed by a
strained bcc Nb(110) structure and
the lattice parameter relaxes after
3 nm.
• RHEED images for the hexagonal
phase at the third atomic layer.
Patterns repeat every 60 deg.
0 deg 30 deg 60 deg
30. Susceptibility AC measurements
• The thinner Nb film exhibits two
steps in the χ’ susceptibility
transition accompanied by two
peaks in the χ’’ susceptibility due
to strained Nb layers at the
interface.
• Growth on a-plane sapphire
initially follows a hexagonal
surface structure to relax the
strain and to stabilize the
subsequent growth of bcc
Nb(110) phase.
• Such initial layers affect the
superconducting properties of
the films and these effects must
be taken into account in the
design of multilayers.
0.1
0.1
0.0
0
0
-1
0.0
-1
7 8 9 10
0.2
0.0
30 nm
100 nm
7 8 9 10
0
-1
''
'
600 nm
Temperature (K)
Temperature (K)
χ(ω)= χ’(ω)+i χ’’(ω)
Strain Effects on the Crystal Growth and Superconducting Properties of Epitaxial Niobium Ultrathin Films, C. Clavero, D. B. Beringer, W.
M. Roach, J. R. Skuza, K. C. Wong, A. D. Batchelor, C. E. Reece, and R. A. Lukaszew, Cryst. Growth Des., 12 (5), pp 2588–2593 (2012)
31. ( a ) 30 nm Nb
200 nm
( b ) 100 nm Nb
200 nm
( c ) 600 nm Nb
400 nm
30
20
10
0
Al 2O3[1100]
600 nm
100 nm
30 nm
Al2O3[0001]
0 500 1000
heigth (nm)
distance (nm)
( d )
Nb [110]
N b [ 001]
Biaxial anisotropy is observed for thicknesses up
to 100 nm while uniaxial anisotropy is observed.
For thicker films
32. Nb growth on (001) MgO
• Nb can also be
epitaxially grown on
(001) MgO surfaces.
• Unexpected findings:
We have found that
depending on the
deposition conditions
it is possible to tailor
different epitaxial
possibilities.
35. Nb (001) on MgO
14.29 nm
0.00 nm
400nm
RRR = 165 RMS = 4.06 nm
>200 RRR values!
36. 30.00 nm
0.00 nm
1.0μm
RMS = 2.90 nm
10.00 nm
0.00 nm
400nm
10.00 nm
0.00 nm
200nm
RMS = 1.21 nm
RMS = 1.08 nm
D. B. Beringer, W. M. Roach, C. Clavero, C. E. Reece, and R. A. Lukaszew, "Roughness analysis applied to niobium thin films
grown on MgO(001) surfaces for superconducting radio frequency cavity applications," Phys. Rev. ST Accel. Beams 16,
022001 (2013).
37. 4 5 6 7 8 9 10
0.0
-0.2
-0.4
-0.6
-0.8
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
"
Temperature (K)
-1.0
4 5 6 7 8 9 10
'
SQUID characterization
Tc = 9.2 K!
Possible loss
due to interfacial
strain
38. Nb on Cu (111)
• Growth at room temperature and annealing at
350 ºC leads to the crystallization of Nb islands
in a hexagonal surface structure, even though
Nb is expected to growth tetragonal (110).
3.3 Å
3.30 Å
0.00 Å
0 Å
Cesar Clavero, Nathan P. Guisinger, Srivilliputhur G. Srinivasan, and R. A. Lukaszew, “Study of Nb epitaxial growth
on Cu(111) at sub-monolayer level”, J. Appl. Phys. 112, 074328 (2012).
39. Nb films on Cu (001) surfaces
(a) RHEED pattern for Nb(110)/Cu(100)/Si(100)
along the Si[100] and Si[110] azimuths. (b) A
representative 2 μm x 2 μm AFM scan for Nb
films on the Cu template.
Possible Nb/Cu(100) epitaxy:
40.
41. SC properties for different growth T
• The films grown at 150 °C have
a very sharp transition from
the superconducting state to
the normal state that begins at
~9 K while films grown at RT
have a much more gradual
transition.
• Our results suggest that an
increased deposition
temperature of Nb onto Cu
leads to films with higher
crystalline quality (grain size)
and thus improved
superconducting properties
(HC1).
Niobium thin film deposition studies on copper surfaces for superconducting radio frequency cavity applications, W. M.
Roach, D. B. Beringer, J. R. Skuza, W. A. Oliver, C. Clavero, C. E. Reece, and R. A. Lukaszew, Phys. Rev. ST Accel. Beams 15,
062002 (2012).
42. Characterization
1. Property that matters (e.g. SRF impedance,
Q, etc)
2. Correlation with microstructure, surface
morphology, DC transport (RRR) and DC
magnetic properties (Hc1)
43. What do we want to know ? How do we find this out ?
What does the sample look like ?
•on a macroscopic scale
•on a microscopic scale
•on an atomic scale
•optical microscopy
•scanning electron microscopy (SEM)
•transmission electron microscopy (TEM)
•scanning probe microscopies (STM, AFM ...)
What is the structure of the sample ?
•internal structure
•density
•microscopic and atomic scales
•X-ray diffraction (XRD)
•low energy electron diffraction (LEED)
•reflection high energy electron diffraction (RHEED)
What is the sample made of ?
•elemental composition
•impurities
•chemical states
•Auger Electron Spectroscopy (AES)
•Energy Dispersive Analysis of X-rays (EDAX)
•X-ray Photoelectron Spectroscopy (XPS)
•Secondary Ion Mass Spectrometry (SIMS)
•Rutherford Backscattering (RBS)
What are the optical properties of the sample ?
•refractive index, absorption
•as a function of wavelength
•ellipsometry
What are the transport properties of the sample?
• resistance
• Surface impedance
•resistance - four point probe
•SIC
What are the mechanical properties of the sample ?
•internal stress in films / substrates
•adhesion
•stress curvature measurements
•adhesion tests
44. Important
• What exactly are we
probing?
– E.g. XRD typically probes
films in the growth
direction. It provides
average microstructure
information.
– E.g. the grain size extracted
from the width of peaks is
along the z-direction.
– RHEED, LEED, TEM provide
local microstructure
information.
– E. g. SEM provides coarser
information regarding
surface morphology than
AFM/STM.
– Optical techniques
(ellipsometry) can provide
information regarding
density of the films.
– It is important to correlate
more than one technique
for complementary
characterization and
acquire a more complete
description of the sample.
45. Good prospects for next SRF films:
Energetic condensation (ECR, HiPIMS)
• As a result of these fundamental
changes, energetic condensation
allows the possibility of
• controlling the following film
properties:
• the density of the film may be
modified to produce improved
optical and corrosion-resistant
coatings
• the film composition can be
changed to produce a range of
hard coatings and low friction
surfaces
• crystal orientation may be
controlled to give the possibility
of low‐temperature epitaxy.
• The additional energy provided by
fast particles arriving at a surface can
induce the following changes to the
film growth process:
– residual gases are desorbed from
the substrate surface
– chemical bonds may be broken
and defects created thus
affecting nucleation processes
and film adhesion
– film morphology changes
– microstructure is altered
– stress in the film is altered
46.
47. Summary
• Higher energetic
condensation offers the
most promise for better
performing SRF films.
• There is sufficient
evidence of better
addition as well as
conformal growth.
• Still needs more R&D to
achieve real “bulk-like”
films!