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1.
CBE Life Sci Educ ; 20(4): ar54, 2021 12.
Artigo em Inglês | MEDLINE | ID: mdl-34546099

RESUMO

Evidence-based teaching practices (EBPs) foster college science, technology, engineering, and mathematics (STEM) students' engagement and performance, yet our knowledge of what contributes to the effectiveness of these practices is less established. We propose a framework that links four social-cognitive variables-students' trust in their instructors, growth mindset, buy-in to instructional practices, and course engagement-to long-standing desired student outcomes of academic performance and intent to persist in science. This framework was tested in classrooms identified as having a high level of EBP implementation with a multi-institutional sample of 2102 undergraduates taught by 14 faculty members. Results indicate that the buy-in framework is a valid representation of college students' learning experiences within EBP contexts overall as well as across underrepresented student groups. In comparison to students' level of growth mindset, students' trust in their instructors was more than twice as predictive of buy-in to how the course was being taught, suggesting that students' views of their instructors are more associated with thriving in a high-EBP course environment than their views of intelligence. This study contributes to the dialogue on transforming undergraduate STEM education by providing a validated student buy-in framework as a lens to understand how EBPs enhance student outcomes.


Assuntos
Estudantes , Confiança , Engenharia , Humanos , Matemática , Ensino , Tecnologia
2.
Age Ageing ; 50(1): 147-152, 2021 01 08.
Artigo em Inglês | MEDLINE | ID: mdl-32500916

RESUMO

AIM: To determine if frailty is associated with poor outcome following in-hospital cardiac arrest; to find if there is a "frailty threshold" beyond which cardiopulmonary resuscitation (CPR) becomes futile. METHODS: Retrospective review of patients aged over 60 years who received CPR between May 2017 and December 2018, in a tertiary referral hospital, which does not provide primary coronary revascularisation. Clinical Frailty Scale (CFS) and Charlson Comorbidity Index were retrospectively assigned. RESULTS: Data for 90 patients were analysed, the median age was 77 (IQR 70-83); 71% were male; 44% were frail (CFS > 4). Frailty was predictive of in-hospital mortality independent of age, comorbidity and cardiac arrest rhythm (OR 2.789 95% CI 1.145-6.795). No frail patients (CFS > 4) survived to hospital discharge, regardless of cardiac arrest rhythm, whilst 13 (26%) of the non-frail (CFS ≤ 4) patients survived to hospital discharge. Of the 13 survivors (Age 72; range 61-86), 12 were alive at 1 year and had a good neurological outcome, the outcome for the remaining patient was unknown. CONCLUSION: Frail patients are unlikely to survive to hospital discharge following in-hospital cardiac arrest, these results may facilitate clinical decision making regarding whether CPR may be considered futile. The Clinical Frailty Scale is a simple bedside assessment that can provide invaluable information when considering treatment escalation plans, as it becomes more widespread, larger scale observations using prospective assessments of frailty may become feasible.


Assuntos
Reanimação Cardiopulmonar , Fragilidade , Idoso , Fragilidade/diagnóstico , Fragilidade/terapia , Humanos , Masculino , Futilidade Médica , Estudos Prospectivos , Estudos Retrospectivos
3.
Artigo em Inglês | MEDLINE | ID: mdl-32742547

RESUMO

The Summer Institutes on Scientific Teaching (SI) is a faculty development workshop in which science, technology, engineering, and mathematics (STEM) instructors, particularly from biology, are trained in the Scientific Teaching (ST) pedagogy. While participants have generally reported positive experiences, we aimed to assess how the SI affected participants' teaching practices. Building on a previously developed taxonomy of ST practices, we surveyed SI participants from the 2004-2014 SI classes regarding specific ST practices. Participants' self-reported use and implementation of ST practices increased immediately after SI attendance as well as over a longer time frame, suggesting that implementation persisted and even increased with time. However, instructors reported implementation gains for some practices more than others. The practices with the highest gains were engaging students in their own learning, using learning goals in course design, employing formative assessment, developing overarching course learning goals, representing science as a process, and facilitating group discussion activities. We propose that the ST practices showing the greatest gains may serve as beneficial focal points for professional development programs, while practices with smaller gains may require modified dissemination approaches or support structures.

4.
ACS Appl Mater Interfaces ; 12(20): 22804-22814, 2020 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-32309922

RESUMO

Atomic layer deposition (ALD) is a well-established technique for depositing nanoscale coatings with pristine control of film thickness and composition. The trimethylaluminum (TMA) and water (H2O) ALD chemistry is inarguably the most widely used and yet to date, we have little information about the atomic-scale structure of the amorphous aluminum oxide (AlOx) formed by this chemistry. This lack of understanding hinders our ability to establish process-structure-property relationships and ultimately limits technological advancements employing AlOx made via ALD. In this work, we employ synchrotron high-energy X-ray diffraction (HE-XRD) coupled with pair distribution function (PDF) analysis to characterize the atomic structure of amorphous AlOx ALD coatings. We combine ex situ and in operando HE-XRD measurements on ALD AlOx and fit these experimental data using stochastic structural modeling to reveal variations in the Al-O bond length, Al and O coordination environment, and extent of Al vacancies as a function of growth conditions. In particular, the local atomic structure of ALD AlOx is found to change with the substrate and number of ALD cycles. The observed trends are consistent with the formation of bulk Al2O3 surrounded by an O-rich surface layer. We deconvolute these data to reveal atomic-scale structural information for both the bulk and surface phases. Overall, this work demonstrates the usefulness of HE-XRD and PDF analysis in improving our understanding of the structure of amorphous ALD thin films and provides a pathway to evaluate how process changes impact the structure and properties of ALD films.

5.
Nano Lett ; 19(8): 5159-5166, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31251069

RESUMO

Thermal atomic layer etching (ALE) was demonstrated on ternary III-V compound semiconductors. In particular, thermal ALE on InGaAs and InAlAs was achieved with sequential, self-limiting fluorination and ligand-exchange reactions using hydrogen fluoride (HF) as the fluorination reactant and dimethylaluminum chloride (DMAC) as the ligand-exchange reactant. Thermal ALE was investigated on planar surfaces and three-dimensional nanostructures. The measured radial etch rates on In0.53Ga0.47As and In0.52Al0.48As vertical nanowires (VNWs) at 300 °C were 0.24 and 0.62 Å/cycle, respectively. An optimized thermal ALE process did not increase the surface roughness after 200 cycles. The etching process also displayed selectivity and orientation dependence. This new thermal ALE process in combination with in situ atomic layer deposition (ALD) was used to fabricate InGaAs gate-all-around structures with minimum width down to 3 nm. The in situ ALE-ALD process produced a sharp vertical MOS interface. Finally, the merits of thermal ALE were demonstrated in the fabrication of n-channel InGaAs FinFETs with record ON-state and OFF-state transistor performance. On the basis of this transistor demonstration, thermal ALE shows great promise for high-volume device manufacturing.

6.
CBE Life Sci Educ ; 18(2): ar22, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-31120395

RESUMO

Evidence-based teaching (EBT), such as active learning and formative assessment, benefits student learning but is not present in many college science classrooms. The choices faculty make about how to teach their science courses are influenced by their personal beliefs and motivations, as well as their departmental structures and institutional cultures. With data from 584 science, technology, engineering, and mathematics (STEM) faculty trained in EBT, we compare which of the following factors most relate to faculty's use of EBT: 1) faculty's personal motivations (e.g., teaching value, confidence, beliefs about intelligence); and 2) their experiences with their institutional teaching environments (e.g., departmental support, student enthusiasm). Faculty's perceived supports in their teaching environments (e.g., having supportive colleagues, being able to access curricular resources) were by far most predictive of their use of EBT. Faculty's personal motivations had little to no relationship when supports were included in these models. The effects were robust, even when controlling for faculty gender, minority status, and teaching experience. Much of the literature has focused on perceived barriers to EBT implementation (e.g., lack of time, constrained teaching space). The current data indicate that a focus on building supports for faculty may have the greatest impact on increasing the presence of EBT in college STEM courses.


Assuntos
Docentes , Aprendizagem Baseada em Problemas , Feminino , Humanos , Masculino , Motivação , Análise de Regressão , Estudantes , Ensino
7.
Int J STEM Educ ; 6(1): 11, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31032173

RESUMO

BACKGROUND: Evidence-based teaching, such as active learning, is associated with increases in student learning and engagement. Although many faculty are beginning to adopt innovative practices, traditional lecture-based teaching tends to dominate college science education. What are the factors associated with faculty's decision to incorporate evidence-based teaching? While there are known barriers that limit adoption of evidence-based practices in science classrooms (e.g., lack of time, student resistance), the present work reveals that instructors' perceptions of supports (e.g., access to teaching resources, encouragement from colleagues) shows a stronger relationship to instructors' use of evidence-based teaching. RESULTS: These results come from a uniquely large dataset of college science faculty and instructors from across the USA (n = 584), who received training in evidence-based teaching. Multiple linear regression analyses of the relationship among perceived supports, barriers, and reported implementation of evidence-based practices showed that instructors report greater implementation when they perceive more social, personal, and resource supports even when barriers are also indicated as present. CONCLUSION: Faculty's perceived supports, not perceived barriers, are most strongly related to their reported implementation of evidence-based teaching. These findings suggest relevant stakeholders devote increased attention identifying and building the factors that promote evidence-based teaching in addition to reducing what inhibits it.

8.
CBE Life Sci Educ ; 17(1)2018.
Artigo em Inglês | MEDLINE | ID: mdl-29378750

RESUMO

There is growing consensus regarding the effectiveness of active-learning pedagogies in college science courses. Less is known about ways that student-level factors contribute to positive outcomes in these contexts. The present study examines students' (N = 245) trust in the instructor-defined as perceptions of their instructor's understanding, acceptance, and care-and students' attitudes toward learning within an anatomy and physiology course featuring active learning. Analyses indicate that student trust of instructor and students' views of their own intelligence are both associated with student commitment to, and engagement in, active learning. Student-reported trust of the instructor corresponded to final grade, while students' views of their own intelligence did not. In an active-learning context in which students are more fully engaged in the learning process, student trust of the instructor was an important contributor to desired student outcomes.


Assuntos
Atitude , Currículo , Aprendizagem Baseada em Problemas , Ciência/educação , Estudantes , Confiança , Universidades , Feminino , Humanos , Masculino , Análise Multivariada , Percepção , Análise de Regressão
9.
Artigo em Inglês | MEDLINE | ID: mdl-33101567

RESUMO

Electron-enhanced atomic layer deposition (EE-ALD) was used to deposit boron nitride (BN) thin films at room temperature and 100 °C using sequential exposures of borazine (B3N3H6) and electrons. Electron-stimulated desorption (ESD) of hydrogen surface species and the corresponding creation of reactive dangling bonds are believed to facilitate borazine adsorption and reduce the temperature required for BN film deposition. In situ ellipsometry measurements showed that the BN film thickness increased linearly versus the number of EE-ALD cycles at room temperature. Maximum growth rates of ~3.2 Å/cycle were measured at electron energies of 80-160 eV. BN film growth was self-limiting versus borazine and electron exposures, as expected for an ALD process. The calculated average hydrogen ESD cross section was σ = 4.2 × 10-17 cm2. Ex situ spectroscopic ellipsometry measurements across the ~1 cm2 area of the BN film defined by the electron beam displayed good uniformity in thickness. Ex situ X-ray photoelectron spectroscopy and in situ Auger spectroscopy revealed high purity, slightly boron-rich BN films with C and O impurity levels <3 at. %. High-resolution transmission electron microscopy (HR-TEM) imaging revealed polycrystalline hexagonal and turbostratic BN with the basal planes approximately parallel to the substrate surface. Ex situ grazing incidence X-ray diffraction measurements observed peaks consistent with hexagonal BN with domain sizes of 1-2 nm. The BN EE-ALD growth rate of ~3.2 Å/cycle is close to the distance of 3.3 Å between BN planes in hexagonal BN. The growth rate and HR-TEM images suggest that approximately one monolayer of BN is deposited for every BN EE-ALD cycle. TEM and scanning TEM/electron energy loss spectroscopy measurements of BN EE-ALD on trenched wafers also showed preferential BN EE-ALD on the horizontal surfaces. This selective deposition on the horizontal surfaces suggests that EE-ALD may enable bottom-up filling of vias and trenches.

10.
CBE Life Sci Educ ; 15(4)2016.
Artigo em Inglês | MEDLINE | ID: mdl-27909026

RESUMO

The benefits of introducing active learning in college science courses are well established, yet more needs to be understood about student buy-in to active learning and how that process of buy-in might relate to student outcomes. We test the exposure-persuasion-identification-commitment (EPIC) process model of buy-in, here applied to student (n = 245) engagement in an undergraduate science course featuring active learning. Student buy-in to active learning was positively associated with engagement in self-regulated learning and students' course performance. The positive associations among buy-in, self-regulated learning, and course performance suggest buy-in as a potentially important factor leading to student engagement and other student outcomes. These findings are particularly salient in course contexts featuring active learning, which encourage active student participation in the learning process.


Assuntos
Currículo , Aprendizagem Baseada em Problemas , Ciência/educação , Estudantes , Universidades , Adolescente , Adulto , Demografia , Feminino , Humanos , Masculino , Modelos Educacionais , Negociação , Adulto Jovem
11.
ACS Appl Mater Interfaces ; 8(28): 18560-9, 2016 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-27351207

RESUMO

This work investigates the use of ozone as a post-treatment of ALD-grown MnO and as a coreactant with bis(ethylcyclopentadienyl)manganese (Mn(EtCp)2) in ALD-like film growth. In situ quartz crystal microbalance measurements are used to monitor the mass changes during growth, which are coupled with ex situ materials characterization following deposition to evaluate the resulting film composition and structure. We determined that during O3 post-treatment of ALD-grown MnO, O3 oxidizes the near-surface region corresponding to a conversion of 22 Å of the MnO film to MnO2. Following oxidation by O3, exposure of Mn(EtCp)2 results in mass gains of over 300 ng/cm(2), which exceeds the expected mass gain for reaction of the Mn(EtCp)2 precursor with surface hydroxyls by over four times. We attribute this high mass gain to adsorbed Mn(EtCp)2 shedding its EtCp ligands at the surface and releasing Mn(II) ions which subsequently diffuse into the bulk film and partially reduce the oxidized film back to MnO. These Mn(EtCp)2 and O3 reactions are combined in sequential steps with (a) Mn(EtCp)2 reacting at the surface of an O-rich layer, shedding its two EtCp ligands and freeing Mn(II) to diffuse into the film followed by (b) O3 oxidizing the film surface and withdrawing Mn from the subsurface to create an O-rich layer. This deposition process results in self-limiting multilayer deposition of crystalline Mn5O8 films with a density of 4.7 g/cm(3) and an anomalously high growth rate of 5.7 Å/cycle. Mn5O8 is a metastable phase of manganese oxide which possesses an intermediate composition between the alternating MnO and MnO2 compositions of the near-surface during the Mn(EtCp)2 and O3 exposures.

12.
J Aging Soc Policy ; 28(3): 187-207, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27010530

RESUMO

This article examines the challenges experienced by very old individuals and their consequences for well-being and mental health. In order to capture unique issues experienced in very old age, 75 participants of the population-based Fordham Centenarian Study answered open-ended questions on everyday challenges. Theme-based coding was then used to categorize and quantify responses. The challenges mentioned most often were challenges faced in the functional (e.g., physical health/activities of daily living restrictions, mobility, sensory impairment), psychological (e.g., loss of well-liked activity, dependency, negative emotions, death), and social (e.g., family loss) life domains. Functional challenges were negatively associated with aging satisfaction and positively associated with loneliness. Psychological challenges were positively linked to aging satisfaction. Social challenges were marginally related to loneliness. Notably, challenges were not related to depression. In conclusion, the challenges experienced in very old age are multidimensional and multifaceted, unique in nature, and have differential relations to mental health. Functional, psychological, and social challenges affect very old individuals' lives and therefore need to be better understood and addressed. Given their consequences, it is imperative for policy makers to develop an awareness for the different types of challenges faced by centenarians, as there may be unique policy implications related to each.


Assuntos
Atividades Cotidianas , Envelhecimento/fisiologia , Envelhecimento/psicologia , Nível de Saúde , Saúde Mental , Idoso de 80 Anos ou mais , Emoções , Feminino , Avaliação Geriátrica , Humanos , Vida Independente , Masculino , Limitação da Mobilidade , Cidade de Nova Iorque , Transtornos de Sensação/fisiopatologia , Apoio Social , Inquéritos e Questionários
13.
Chem Mater ; 282016.
Artigo em Inglês | MEDLINE | ID: mdl-31092972

RESUMO

Low energy electrons may provide mechanisms to enhance thin film growth at low temperatures. As a proof of concept, this work demonstrated the deposition of gallium nitride (GaN) films over areas of ∼5 cm2 at room temperature and 100 °C using electrons with a low energy of 50 eV from an electron flood gun. The GaN films were deposited on Si(111) wafers using a cycle of reactions similar to the sequence employed for GaN atomic layer deposition (ALD). Trimethylgallium (Ga(CH3)3, TMG), hydrogen (H) radicals and ammonia (NH3) were employed as the reactants with electron exposures included in the reaction cycle after the TMG/H and NH3 exposures. A number of ex situ techniques were then employed to analyze the GaN films. Spectroscopic ellipsometry measurements revealed that the GaN films grew linearly with the number of reaction cycles. Linear growth rates of up to 1.3 Å/ cycle were obtained from the surface areas receiving the highest electron fluxes. Grazing incidence X-ray diffraction analysis revealed polycrystalline GaN films with the wurtzite crystal structure. Transmission electron microscopy (TEM) images showed crystalline grains with diameters between 2 and 10 nm depending on the growth temperature. X-ray photoelectron spectroscopy depth-profiling displayed no oxygen contamination when the GaN films were capped with Al prior to atmospheric exposure. However, the carbon concentrations in the GaN films were 10-35 at. %. The mechanism for the low temperature GaN growth is believed to result from the electron stimulated desorption (ESD) of hydrogen. Hydrogen ESD yields dangling bonds that facilitate Ga-N bond formation. Mass spectrometry measurements performed concurrently with the reaction cycles revealed increases in the pressure of H2 and various GaN etch products during the electron beam exposures. The amount of H2 and GaN etch products increased with electron beam energy from 25 to 200 eV. These results indicate that the GaN growth occurs with competing GaN etching during the reaction cycles.

14.
Artigo em Inglês | MEDLINE | ID: mdl-26734395

RESUMO

Junior doctors frequently rely on electronic access to clinical guidelines to inform assessment and management, particularly whilst on-call and occasionally during emergencies. Difficulties in locating and accessing up to date guidance from different hospital intranet sites can lead to delays or errors in patient management. We used a focus group and email feedback to redesign an intranet site for junior doctors which logically organised the documents which doctors said they needed access to in one readily accessible location. A quality improvement project was carried out over six months, testing two iterations of the new junior doctors' intranet site before a third version was launched and evaluated. Their performance was measured by the number of mouse clicks and the time required for doctors to find a representative subset of five guidelines, and revisions were made at each cycle based on feedback from doctors and stakeholders. Cumulatively, we demonstrated a decrease in the total number of clicks required to access the sample of guidelines from 18 to 12 clicks, a corresponding decrease in the time required to access the sample of guidelines from 130 seconds to 22 seconds, and an increase in user satisfaction. We maintained one-click access to emergency guidance. In conclusion, we have developed and implemented an electronic resource for junior doctors which provides more immediate access to both emergency and non-emergency clinical guidance. To ensure the resource remains up to date, it will be maintained by Foundation Programme representatives at our hospital on a rolling basis.

15.
Nano Lett ; 12(7): 3706-10, 2012 Jul 11.
Artigo em Inglês | MEDLINE | ID: mdl-22716769

RESUMO

In this paper, a method is presented to create and characterize mechanically robust, free-standing, ultrathin, oxide films with controlled, nanometer-scale thickness using atomic layer deposition (ALD) on graphene. Aluminum oxide films were deposited onto suspended graphene membranes using ALD. Subsequent etching of the graphene left pure aluminum oxide films only a few atoms in thickness. A pressurized blister test was used to determine that these ultrathin films have a Young's modulus of 154 ± 13 GPa. This Young's modulus is comparable to much thicker alumina ALD films. This behavior indicates that these ultrathin two-dimensional films have excellent mechanical integrity. The films are also impermeable to standard gases suggesting they are pinhole-free. These continuous ultrathin films are expected to enable new applications in fields such as thin film coatings, membranes, and flexible electronics.

16.
Langmuir ; 27(24): 15155-64, 2011 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-22029704

RESUMO

Molecular layer deposition (MLD) of aluminum alkoxide polymer films was examined using trimethlyaluminum (TMA) and glycidol (GLY) as the reactants. Glycidol is a high vapor pressure heterobifunctional reactant with both hydroxyl and epoxy chemical functionalites. These two different functionalities help avoid "double reactions" that are common with homobifuctional reactants. A variety of techniques, including in situ Fourier transform infrared (FTIR) spectroscopy and quartz crystal microbalance (QCM) measurements, were employed to study the film growth. FTIR measurements at 100 and 125 °C observed the selective reaction of the GLY hydroxyl group with the AlCH(3) surface species during GLY exposure. Epoxy ring-opening and methyl transfer from TMA to the surface epoxy species were then monitored during TMA exposure. This epoxy ring-opening reaction is dependent on strong Lewis acid-base interactions between aluminum and oxygen. The QCM experiments observed linear growth with self-limiting surface reactions at 100-175 °C under certain growth conditions. With a sufficient purge time of 20 s after TMA and GLY exposures at 125 °C, the mass gain per cycle (MGPC) was 19.8 ng/cm(2)-cycle. The individual mass gains after the TMA and GLY exposures were also consistent with a TMA/GLY stoichiometry of 4:3 in the MLD film. This TMA/GLY stoichiometry suggests the presence of Al(2)O(2) dimeric core species. The MLD films resulting from these TMA and GLY exposures also evolved with annealing temperature to form thinner conformal porous films with increased density. Non-self-limiting growth was a problem at shorter purge times and lower temperatures. With shorter purge times of 10 s at 125 °C, the MPGC increased dramatically to 134 ng/cm(2)-cycle. The individual mass gains after the TMA and GLY exposures in the CVD regime were consistent with a TMA/GLY stoichiometry of 1:1. The MGPC decreased progressively versus purge time. This behavior was attributed to the removal of reactants that could lead to CVD and the instability of the surface species after the reactant exposures. These results reveal that the TMA and GLY reaction displays much complexity and must be carefully controlled to be a useful MLD process.

17.
J Am Chem Soc ; 133(37): 14741-54, 2011 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-21797223

RESUMO

Passivating lithium ion (Li) battery electrode surfaces to prevent electrolyte decomposition is critical for battery operations. Recent work on conformal atomic layer deposition (ALD) coating of anodes and cathodes has shown significant technological promise. ALD further provides well-characterized model platforms for understanding electrolyte decomposition initiated by electron tunneling through a passivating layer. First-principles calculations reveal two regimes of electron transfer to adsorbed ethylene carbonate molecules (EC, a main component of commercial electrolyte), depending on whether the electrode is alumina coated. On bare Li metal electrode surfaces, EC accepts electrons and decomposes within picoseconds. In contrast, constrained density functional theory calculations in an ultrahigh vacuum setting show that, with the oxide coating, e(-) tunneling to the adsorbed EC falls within the nonadiabatic regime. Here the molecular reorganization energy, computed in the harmonic approximation, plays a key role in slowing down electron transfer. Ab initio molecular dynamics simulations conducted at liquid EC electrode interfaces are consistent with the view that reactions and electron transfer occur right at the interface. Microgravimetric measurements demonstrate that the ALD coating decreases electrolyte decomposition and corroborates the theoretical predictions.

18.
Nano Lett ; 11(2): 414-8, 2011 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-21166425

RESUMO

To deploy Li-ion batteries in next-generation vehicles, it is essential to develop electrodes with durability, high energy density, and high power. Here we report a breakthrough in controlled full-electrode nanoscale coatings that enables nanosized materials to cycle with durable high energy and remarkable rate performance. The nanoparticle electrodes are coated with Al(2)O(3) using atomic layer deposition (ALD). The coated nano-LiCoO(2) electrodes with 2 ALD cycles deliver a discharge capacity of 133 mAh/g with currents of 1400 mA/g (7.8C), corresponding to a 250% improvement in reversible capacity compared to bare nanoparticles (br-nLCO), when cycled at this high rate. The simple ALD process is broadly applicable and provides new opportunities for the battery industry to design other novel nanostructured electrodes that are highly durable even while cycling at high rate.


Assuntos
Cobalto/química , Fontes de Energia Elétrica , Eletrodos , Membranas Artificiais , Nanoestruturas/química , Nanotecnologia/instrumentação , Óxidos/química , Automóveis , Cristalização/métodos , Desenho de Equipamento , Análise de Falha de Equipamento , Nanoestruturas/ultraestrutura , Tamanho da Partícula
19.
Chemphyschem ; 11(10): 2124-30, 2010 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-20449864

RESUMO

An alumina surface coating is demonstrated to improve electrochemical performance of MoO(3) nanoparticles as high capacity/high-volume expansion anodes for Li-ion batteries. Thin, conformal surface coatings were grown using atomic layer deposition (ALD) that relies on self-limiting surface reactions. ALD coatings were tested on both individual nanoparticles and prefabricated electrodes containing conductive additive and binder. The coated and non-coated materials were characterized using transmission electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and galvanostatic charge/discharge cycling. Importantly, increased stability and capacity retention was only observed when the fully fabricated electrode was coated. The alumina layer both improves the adhesion of the entire electrode, during volume expansion/contraction and protects the nanoparticle surfaces. Coating the entire electrode also allows for an important carbothermal reduction process that occurs during electrode pre-heat treatment. ALD is thus demonstrated as a novel and necessary method that may be employed to coat the tortuous network of a battery electrode.

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