Name: cooling rate dependent ellipsometry measurements to determine the dynamics of thin glassy films
Uploaded: 2016-01-26T18:00:00.000+00:00
Duration: 9 min 32 s
Description: Watch this Scientific Journal Video about Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films at JoVE.com

Os autores gostariam de agradecer James A. Forrest ajuda para a idéia inicial para esta técnica. 26 Este trabalho foi apoiado pelo financiamento da Universidade da Pensilvânia e foi parcialmente financiado pelo programa MRSEC da National Science Foundation sob concessão não. DMR-11- 20901, da Universidade da Pensilvânia.

1. Preparação de Cinema <ol><li> Pesar 0,04 g de poliestireno, e colocar num frasco de 30 ml. </li><li> Pesar 2 g de tolueno para dentro do frasco. Uma solução a 2% em peso de poliestireno em tolueno produz um filme de cerca de 100 nm. </li><li> Deixe a solução sit O / N para dissolver totalmente o poliestireno e deixar que as soluções resolver. </li><li> Coloque uma pastilha de 1 cm x 1 cm de silício (Si) para um Revestidor rotação. </li><li> Girar a bolacha a 8.000 rpm durante 45 seg. Enquanto está girando, gota cerca de 1 ml de tolueno na bolacha de fiação. Nota: Todas as etapas que envolvem o revestimento de spin são realizadas em uma coifa. </li><li> Por agora estacionária bolacha de Si, adicionar a solução do passo 1.3, gota a gota sobre a bolacha de Si até que toda a superfície da bolacha de Si é coberto. </li><li> Antes de a solução seque sobre a bolacha, girar a bolacha de Si a 4.000 rpm durante 20 segundos. </li><li> Determinar a espessura do filme utilizando elipsometria (ver Passo 2). </li><li> Se o filme é a espessura desejada, Anneal a película numa estufa de vácuo a 393 K durante 15 horas. </li></ol> 2. Determinar espessura de filme <ol><li> Coloque o filme fundido girou para o palco elipsómetro e medir os ângulos ellipsometric Ψ (λ) e Δ (λ) em um ângulo de luz incidente de 70 ° com um tempo de aquisição de 1 seg e a definição de fuso média ligado. </li><li> Utilizando o software de elipsometria, encaixar o Ψ resultante (λ) e dados Δ (λ) a um modelo de três camadas de acordo com o protocolo do fabricante. Não há entradas adicionais do usuário. A primeira camada é uma camada de substrato de Si, a segunda camada é uma camada de óxido nativo com uma espessura de 1,5 nm, e a terceira camada é um modelo de Cauchy (N = A + B / λ 2, k = 0), o que corresponde para as propriedades ópticas da película de poliestireno. Neste modelo, A e B são parâmetros de ajuste, e n e k são as componentes reais e imaginários do índice de refracção de o, respectivamente. </li><li> Para a camada de Cauchy, caber a thickness e os parâmetros A e B se o filme for superior a 10 nm. Se o filme for inferior a 10 nm, só cabem A. Nota: Isso será discutido mais adiante na seção Resultados Representante. </li></ol> 3. Taxa de resfriamento T Dependente g Medidas <ol><li> Revestir a superfície do elemento de aquecimento da etapa de temperatura variável elipsómetro com pasta térmica. </li><li> Coloque a película de poliestireno recozido sobre o elemento de aquecimento. </li><li> Apertar a película firmemente sobre o elemento de aquecimento. </li><li> Fluxo de 100% de gás de azoto seco através da fase de temperatura a uma pressão de &lt;69 kPa. </li><li> Utilizando o software de fase temperatura, criação de um perfil de temperatura. Este perfil de temperaturas inicia-se com uma rampa de aquecimento de 393 K a 150 K / min. Segurar a película no 393K durante 20 min. <ol><li> Em seguida, as rampas de arrefecimento alternativos para 293 K em taxas de 150, 120, 90, 60, 30, 10, 7, 3, 1 e K / min, com rampas de aquecimento a 393 K a 150 K / min. Coloque a 5 min temperature espera depois de cada rampa. </li></ol></li><li> No software elipsometria, fazer um modelo elipsometria dependente da temperatura semelhante à da secção 2. Todas as três camadas são os mesmos, excepto que o substrato é alterado para um modelo de Si dependente da temperatura. </li><li> Na camada para o modelo Si dependente da temperatura, ative a opção &quot;Usar Ext Temp de Parm Log&quot; Parameter. </li><li> Usando equipamentos de laboratório software controlador, tem o software elipsómetro ler os valores de temperatura do estágio de temperatura. </li><li> Alinhar a elipsometria de tal modo que o sinal atinge a máxima intensidade. </li><li> Em &quot;Configurações Editar hardware&quot;, defina o tempo de aquisição rápida de 1 segundo com zona de alta precisão média. Defina o tempo normal de aquisição de 3 segundos com zona de alta precisão média. </li><li> Sob o &quot;in situ&quot; guia no software elipsómetro verificar o &quot;modo de aquisição rápido tempo de&quot; caixa e pressione &quot;Start Acquisition&quot;. Em seguida, inicieo perfil de temperatura. Antes da rampa de 3 K / min de arrefecimento, desmarque a caixa rápido tempo de aquisição. </li></ol> 4. Determinação de valores de T g <ol><li> Exportar a temperatura e perfis de espessura para a gráfica e software de análise preferido, e separar os dados de temperatura e espessura para todas as taxas de resfriamento 9. </li><li> A fim de explicar o efeito da zona média durante a aquisição da temperatura, tomar todos os valores de temperatura, e média, com o valor de temperatura que o precede, tais que T = (T i + t i-1) / 2, em que T I é um valor de temperatura num determinado momento, e T I-1 é a temperatura do ponto de tempo anterior. </li><li> Plot Espessura vs. temperatura para cada taxa de resfriamento. </li><li> Executar um ajuste linear sobre uma parte do regime de líquido super arrefecida (o regime de temperatura elevada com o coeficiente de dilatação maior). Este regime será de cerca de 393 K e 380 K. </li><li> PerfoRM um ajuste linear sobre uma parte do regime de vítreo que mesmo conjunto de dados. Este regime tem um coeficiente de dilatação inferior, e será a partir de cerca de 293 K e 340 K. </li><li> Encontre o ponto de intersecção dessas duas linhas. A temperatura onde estas linhas se cruzam representa a temperatura de transição vítrea. </li><li> Faça isso para todas as nove rampas. </li></ol> 5. Analisando Média Thin Film Dynamics <ol><li> Para um determinado lote de espessura de filme Log (resfriamento Rate (K / min)) vs. 1 / T g (K-1). </li><li> Compare isso indiretamente à medição da massa e de superfície dinâmica dirigir pela relação empírica: Arrefecimento Rate * τ α = 1000. 23,24 </li></ol>

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The Authors have no conflicts of interest to disclose.

Arrefecimento da taxa de medições g T dependentes são experiências de caracterização de alto rendimento que podem determinar a Tg, o coeficiente de dilatação do vidro e o líquido super-resfriado, a dependência da temperatura da dinâmica médios, e a fragilidade de um material vítreo particular numa experiência única. Além disso, ao contrário de fluorescência, a incorporação, ou experiências de relaxação nanohole, g experiências CR-T são relativamente simples e rá...

O trabalho seminal de Keddie Jones e Corey 1 mostrou que a temperatura de transição vítrea (Tg) dos filmes finos de poliestireno ultra-diminui em relação ao valor de grandes quantidades a uma espessura inferior a 60 nm. Desde então, diversos estudos experimentais 2-11 apoiaram a hipótese de que as reduções observadas na Tg são causadas por uma camada de mobilidade aumentada próximo da superfície livre desses filmes. No entanto, estas experiências são medidas indirectas de um único tempo de relaxamento, e, portanto, existe um debate 12- 18 centrado sobre uma correlação directa entre o número de dinâmica de película fina e da dinâmica na interface ar / polímero. Para responder a este debate, muitos estudos têm medido diretamente a dinâmica da superfície livre (superfície τ). Incorporação de nanopartículas, 19,20 nanohole relaxamento, 21 e 22 de fluorescência estudos mostram que o ar / polímero de interface hcomo dinâmica ordens de grandeza mais rápido do que o tempo de relaxamento alfa granel (τ α) com uma dependência da temperatura muito mais fraca do que a de τ α. Devido à sua fraca dependência da temperatura, a superfície τ desses filmes, 19-22 e dinâmica melhoradas de filmes finos de poliestireno, 23,24 intersecta o relaxamento alfa granel (τ ct) a um único ponto T *, o qual é poucos graus acima T g, e a uma α τ ≈ de 1 seg. A presença de T * poderia explicar por que experiências que sondam tempos de relaxação mais rápido do que * não conseguem ver qualquer dependência espessura na T g de filmes ultrafinos de poliestireno. 13-18 Por último, enquanto medições diretas da camada reforçada espetáculo móvel que tem uma espessura de 4-8 nm, 20-22, há evidências de que o comprimento de propagação da dinâmica na interface ar / polímero é muito maior do que a espessura da superfície móvel Layer. 5,25-26 Este relatório tem como objetivo descrever completamente um protocolo para o uso de elipsometria para o arrefecimento da taxa dependente T g (CR-T g) experimentos. CR-Tg foram anteriormente utilizados para descrever a dinâmica médios de filmes ultra-finos de poliestireno. 23,24,27,28 Além disso, esta técnica foi usada recentemente para mostrar uma correlação directa entre a dinâmica médios em filmes ultrafinos de poliestireno , e a dinâmica na superfície livre 23 A vantagem de CR-T medições de g sobre outros tipos de medições, tais como fluorescência, nanopartículas incorporação, nanohole relaxamento, nanocalorimetry, espectroscopia de dieléctrico, e de Brillouin espalhamento de luz., estudos é que eles são relativamente rápidos e experiências simples que não utilizam fluoróforos ou outras técnicas experimentais complicados. Os avanços recentes em elipsometria espectroscópica permitir que esta técnica para ser utilizado para determinar a eficiência óptica properts de filmes ultra-finos de polímeros e outros tipos de materiais híbridos com precisão excepcional. Como tal, esta técnica investiga a dinâmica médios de filmes finos tecnologicamente aplicável em regimes de temperatura e de tempo relevantes para a transição vítrea (Tg ≤, τ α ≥ 100 seg). Além disso, esta técnica fornece informação sobre os coeficientes de expansão do vítreo e ceia arrefecida estados líquidos, assim como a fragilidade do sistema, o qual pode então ser comparado com os dados para os filmes a granel. Finalmente, experiências g CR T pode ser usado para qualquer sistema vítreo, desde que a integridade da película mantém-se durante todo o experimento.

<table><tbody><tr><td>Toluene</td><td>Sigma Aldrich</td><td>179418-1L</td><td>This can be purchased from any chemical company.</td></tr><tr><td>Atactic Polystyrene</td><td>Polymer Source Inc.</td><td>P-4092-S</td><td>This can be purchased from any chemical company.</td></tr><tr><td>THMS 600 temperature stage</td><td>Linkam</td><td>THMS 600</td><td>any temperature stage that can be fit to an ellipsometer could be used.</td></tr><tr><td>M2000V Spectroscopic Ellipsometer</td><td>J.A. Woollam</td><td>M200V</td><td>This procedure should be applicable for any spectroscopic ellipsometer.</td></tr><tr><td>Spin Coater</td><td>Laurell Technologies</td><td>WS-650-23B</td><td>This Procedure is possible with any spin coater</td></tr><tr><td>Sample vials</td><td>Fisher Scientific</td><td>02-912-379</td><td>Any sample vials will do</td></tr><tr><td>Silicon wafers</td><td>Virginia semi conductors</td><td>325S1410694D</td><td></td></tr></tbody></table>

cooling rate dependent ellipsometry measurements to determine the dynamics of thin glassy films

Este relatório tem como objetivo descrever totalmente a técnica experimental de usar elipsometria para o arrefecimento da taxa dependente T g (CR-T g) experimentos. Estas medições são experiências de caracterização de alto rendimento simples, que pode determinar a temperatura de transição vítrea (T g), dinâmica médios, fragilidade e o coeficiente de expansão dos estados líquido e super-arrefecida vítreos para uma variedade de materiais vítreos. Esta técnica permite a estes parâmetros a serem medidos numa única experiência, enquanto que outros métodos de combinar uma variedade de técnicas diferentes para investigar todas estas propriedades. As medições da dinâmica fechar a Tg é particularmente difícil. A vantagem da taxa de resfriamento medições dependentes T g ao longo de outros métodos que sondam directamente dinâmica a granel e de relaxação de superfície é que elas são experiências relativamente rápida e simples, que não utilizam fluoróforos ou outro ex complicadotécnicas rimentais. Além disso, esta técnica de sondas médias a dinâmica de películas finas tecnologicamente relevantes de temperatura e tempo de relaxação (τ α) que sejam relevantes para a transição de vidro (τ α&gt; 100 seg). A limitação ao uso de elipsometria de arrefecimento de taxa dependente T g experiências é que ele não pode sondar tempos de relaxação relevantes para medições de viscosidade (τ α &lt;&lt; 1 seg). Outras técnicas de medição dependente T g da taxa de arrefecimento, no entanto, pode estender o método g CR-T para tempos de relaxação mais rápidos. Além disso, esta técnica pode ser usado para qualquer sistema vítreo, desde que a integridade da película mantém-se durante todo o experimento.

Fitting Raw Elipsometria Dados Filmes de poliestireno são transparentes na faixa de comprimento de onda da elipsómetro (500-1,600 nm). Assim, um modelo de Cauchy é um bom modelo para descrever o índice de refracção das películas de poliestireno. A Figura 1A mostra um exemplo de Ψ (λ) e Δ (λ) para uma espessura (274 nm) de filme de poliestireno, e o ajuste resultante à modelo Cauchy...

Watch this Scientific Journal Video about Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films at JoVE.com

Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

Aqui, apresentamos um protocolo para o arrefecimento das taxas de experimentos dependentes elipsometria, que pode determinar a temperatura de transição vítrea (Tg), dinâmica de fragilidade e médios, o coeficiente de expansão do líquido super-resfriado e vidro para uma variedade de materiais vítreos.

Arrefecimento Medidas de freqüência Elipsometria Dependentes para determinar a dinâmica de finas Glassy Films

This report aims to fully describe the experimental technique of using ellipsometry for cooling rate dependent Tg (CR-Tg) experiments. These measurements ...

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Chemistry

8.1K visualizações.  University of Pennsylvania.  Aqui, apresentamos um protocolo para o arrefecimento das taxas de experimentos dependentes elipsometria, que pode determinar a temperatura de transição vítrea (Tg), dinâmica de fragilidade e médios, o coeficiente de expansão do líquido super-resfriado e vidro para uma variedade de materiais vítreos. 

Vídeo: Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities &#8211; high spatial resolution and richness of microstructural data &#8211; with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

The use of electron channeling contrast imaging in a scanning electron microscope to characterize defects in III-V/Si heteroexpitaxial thin films is described. This method yields similar results to plan-view transmission electron microscopy, but in significantly less time due to lack of required sample preparation.

Electron Canalização Contraste de imagem para Rápido III-V heteroepitaxiais Caracterização

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

Engenharia

Formation of Thick Dense Yttrium Iron Garnet Films Using Aerosol Deposition

Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% of the bulk. The primary advantage of AD is that the deposition takes place entirely at ambient temperature; thereby enabling film growth in material systems with disparate melting temperatures. This report describes in detail the processing steps for preparing the powder and for performing AD using the custom-built system. Representative characterization results are presented from scanning electron microscopy, profilometry, and ferromagnetic resonance for films grown in this system. As a representative overview of the capabilities of the system, focus is given to a sample produced following the described protocol and system setup. Results indicate that this system can successfully deposit 11 &#181;m thick yttrium iron garnet films that are &#160;&#62; 90% of the bulk density during a single 5 min deposition run. A discussion of methods to afford better control of the aerosol and particle selection for improved thickness and roughness variations in the film is provided.

This report describes the use of a custom-built system to perform aerosol deposition of thick films of yttrium iron garnet onto sapphire substrates at RT. The deposited films are characterized using scanning electron microscopy, profilometry, and ferromagnetic resonance to give a representative overview of the capabilities of the technique.

Formação de espessas densas ítrio Ferro Garnet Films Usando Aerosol Deposição

Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% ...

High-resolution Thermal Micro-imaging Using Europium Chelate Luminescent Coatings

Micro-electronic devices often undergo significant self-heating when biased to their typical operating conditions. This paper describes a convenient optical micro-imaging technique which can be used to map and quantify such behavior. Europium thenoyltrifluoroacetonate (EuTFC) has a 612 nm luminescence line whose activation efficiency drops strongly with increasing temperature, due to T-dependent interactions between the Eu3+ ion and the organic chelating compound. This material may be readily coated on to a sample surface by thermal sublimation in vacuum. When the coating is excited with ultraviolet light (337 nm) an optical micro-image of the 612 nm luminescent response can be converted directly into a map of the sample surface temperature. This technique offers spatial resolution limited only by the microscope optics (about 1 micron) and time resolution limited by the speed of the camera employed. It offers the additional advantages of only requiring comparatively simple and non-specialized equipment, and giving a quantitative probe of sample temperature.

Europium thenoyltrifluoroacetonate (EuTFC) has an optical luminescence line at 612 nm, whose activation efficiency decreases strongly with temperature. If a sample coated with a thin film of this material is micro-imaged, the 612 nm luminescent response intensity may be converted into a direct map of sample surface temperature.

High-resolution Micro-imagem térmica Usando európio quelato luminescentes Coatings

Micro-electronic devices often undergo significant self-heating when biased to their typical operating conditions. This paper describes a convenient ...

Electrospray Deposition of Uniform Thickness Ge23Sb7S70 and As40S60 Chalcogenide Glass Films

Solution-based electrospray film deposition, which is compatible with continuous, roll-to-roll processing, is applied to chalcogenide glasses. Two chalcogenide compositions are demonstrated: Ge23Sb7S70 and As40S60, which have both been studied extensively for planar mid-infrared (mid-IR) microphotonic devices. In this approach, uniform thickness films are fabricated through the use of computer numerical controlled (CNC) motion. Chalcogenide glass (ChG) is written over the substrate by a single nozzle along a serpentine path. Films were subjected to a series of heat treatments between 100 &#176;C and 200 &#176;C under vacuum to drive off residual solvent and densify the films. Based on transmission Fourier transform infrared (FTIR) spectroscopy and surface roughness measurements, both compositions were found to be suitable for the fabrication of planar devices operating in the mid-IR region. Residual solvent removal was found to be much quicker for the As40S60 film as compared to Ge23Sb7S70. Based on the advantages of electrospray, direct printing of a gradient refractive index (GRIN) mid-IR transparent coating is envisioned, given the difference in refractive index of the two compositions in this study.

Electrospray Deposition of Uniform Thickness Ge23Sb7S70 and As40S60 Chalcogenide Glass Films

A method of uniform thickness solution-derived chalcogenide glass film deposition is demonstrated using computer numerical controlled motion of a single-nozzle electrospray.

Electrospray Deposição de espessura uniforme, Ge<sub&gt; 23</sub&gt; Sb<sub&gt; 7</sub&gt; S<sub&gt; 70</sub&gt; E Como<sub&gt; 40</sub&gt; S<sub&gt; 60</sub&gt; Films vidro chalcogenide

Solution-based electrospray film deposition, which is compatible with continuous, roll-to-roll processing, is applied to chalcogenide glasses. Two ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.

Recombinação Dynamics em Thin-film materiais fotovoltaicos via Condutividade Microondas resolvida no tempo

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90&#176; between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Here, we present a protocol to trigger an orientational transition of a liquid crystal in response to temperature. Methodologies are described for preparing a sample in order to observe the transition and the detailed transitional evolution.

Transição Orientacional em Cristal Líquido Ativada pelo Crescimento Termodinâmico de Folhas Múltiplas Interfaciais

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

Measuring the Densities of Aqueous Glasses at Cryogenic Temperatures

We demonstrate a method for determining the vitreous phase cryogenic temperature densities of aqueous mixtures, and other samples that require rapid cooling, to prepare the desired cryogenic temperature phase. Microliter to picoliter size drops are cooled by projection into a liquid nitrogen-argon (N2-Ar) mixture. The cryogenic temperature phase of the drop is evaluated using a visual assay that correlates with X-ray diffraction measurements. The density of the liquid N2-Ar mixture is adjusted by adding N2 or Ar until the drop becomes neutrally buoyant. The density of this mixture and thus of the drop is determined using a test mass and Archimedes principle. With appropriate care in drop preparation, management of gas above the liquid cryogen mixture to minimize icing, and regular mixing of the cryogenic mixture to prevent density stratification and phase separation, densities accurate to &#60;0.5% of drops as small as 50 pL can readily be determined. Measurements on aqueous cryoprotectant mixtures provide insight into cryoprotectant action, and provide quantitative data to facilitate thermal contraction matching in biological cryopreservation.

A protocol for determining the vitreous phase densities of micro- to pico-liter size drops of aqueous mixtures at cryogenic temperatures is described.

Medindo as densidades de vidros aquosos em temperaturas criogênicas

We demonstrate a method for determining the vitreous phase cryogenic temperature densities of aqueous mixtures, and other samples that require rapid ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

Preparação das redes de cristal líquido para macroscópica movimento oscilatório induzido pela luz

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (Cu variant) entropy-stabilized oxides. Phase pure and chemically homogeneous (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) ceramic pellets are synthesized and used in the deposition of ultra-high quality, phase pure, single crystalline thin films of the target stoichiometry. A detailed methodology for the deposition of smooth, chemically homogeneous, entropy-stabilized oxide thin films by pulsed laser deposition on (001)-oriented MgO substrates is described. The phase and crystallinity of bulk and thin film materials are confirmed using X-ray diffraction. Composition and chemical homogeneity are confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface topography of thin films is measured with scanning probe microscopy. The synthesis of high quality, single crystalline, entropy-stabilized oxide thin films enables the study of interface, size, strain, and disorder effects on the properties in this new class of highly disordered oxide materials.

The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

Granel e síntese de película fina de óxidos de entropia-estabilizado em termos de composição variantes

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and ...

Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous studies on flowing liquid films have neglected the contributions of spatial structures of waves to the impact outcome, while this has recently been shown to have a significant influence on the drop impact dynamics. In this report, we outline a step-by-step procedure to investigate the effect of periodic inlet forcing of a flowing liquid film leading to the production of spatiotemporally regular wave structures on drop impact dynamics. A function generator in connection with a solenoid valve is used to excite these spatiotemporally regular wave structures on the film surface while the impact dynamics of uniform-sized droplets are captured using a high-speed camera. Three distinct regions are then studied; viz. the capillary wave region preceding the large wave peak, the flat film region, and the wave hump region. The effects of important dimensionless quantities such as film Reynolds, drop Weber and Ohnesorge numbers parameterized by the film flow rate, drop speed, and drop size are also examined. Our results show interesting, hitherto undiscovered dynamics brought about by this application of film inlet forcing of the flowing film for both low and high inertia drops.

A protocol to study the contributions of waves to droplet impact dynamics on flowing liquid films is presented.

Controle de filme para estudar as contribuições das ondas a dinâmica de impacto da gota em filmes líquido fluindo fino

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous ...