arXiv subjects

Camille Bishop

Publications and source records attributed to Camille Bishop.

5 recordsLinked to original sources

arXiv2026

Over what length scale does an inorganic substrate perturb the structure of a glassy organic semiconductor?

While the bulk structure of vapor-deposited glasses has been extensively studied, structure at buried interfaces has received little attention, despite being important for organic electronic applications. To learn about glass structure at buried interfaces, we study the structure of vapor-deposited glasses of the organic semiconductor DSA-Ph (1,4-di-[4-(N,N-diphenyl)amino]styryl-benzene) as a function of film thickness; structure is probed with grazing incidence X-ray scattering. We deposit on silicon and gold substrates and span a film thickness range of 10-600 nm. Our experiments demonstrate that interfacial molecular packing in vapor-deposited glasses of DSA-Ph is more disordered compared to the bulk. At a deposition temperature near room temperature, we estimate ~ 8 nm near the substrate can have modified molecular packing. Molecular dynamics simulations of a coarse-grained representation of DSA-Ph reveal a similar length scale. In both the simulations and the experiments, deposition temperature controls glass structure beyond this interfacial layer of a few nanometers.

cond-mat.mtrl-sci↗

arXiv2026

Stable Glasses of Organic Semiconductor Resist Crystallization

The instability of glassy solids poses a key limitation to their use in several technological applications. Well-packed organic glasses, prepared by physical vapor deposition (PVD), have drawn attention recently because they can exhibit significantly higher thermal and chemical stability than glasses prepared from more traditional routes. We show here that PVD glasses can also show enhanced resistance to crystallization. By controlling the deposition temperature, resistance towards crystallization can be enhanced by at least a factor of ten in PVD glasses of the model organic semiconductor Alq3 (Tris(8-hydroxyquinolinato) aluminum). PVD glasses of Alq3 first transform into a supercooled liquid before crystallizing. By controlling the deposition temperature, we increase the glass to liquid transformation time thereby also increasing the overall time for crystallization. We thus demonstrate a new strategy to stabilize glasses of organic semiconductors against crystallization, which is a common failure mechanism in OLED (organic light emitting diode) devices.

cond-mat.mtrl-sci↗

arXiv2026

Using Deposition Rate and Substrate Temperature to Manipulate Liquid Crystal-like Order in a Vapor-deposited Hexagonal Columnar Glass

We investigate vapor-deposited glasses of a phenanthroperylene-ester, known to form an equilibrium hexagonal columnar phase, and show that liquid crystal-like order can be manipulated by the choice of deposition rate and substrate temperature during deposition. We find that rate-temperature superposition (RTS), the equivalence of lowering deposition rate and raising substrate temperature, can be used to predict and control the molecular orientation in vapor-deposited glasses over a wide range of substrate temperatures (0.75Tg to 1.0Tg). This work extends RTS to a new structural motif, hexagonal columnar liquid crystal order, which is being explored for organic electronics applications. By several metrics, including the apparent average face-to-face nearest-neighbor distance, PVD glasses of the phenanthroperylene-ester are as ordered as the glass prepared by cooling the equilibrium liquid crystal. By other measures, the PVD glasses are less ordered than the cooled liquid crystal. We explain the difference in the maximum attainable order with the existence of a gradient in molecular mobility at the free surface of a liquid crystal, and its impact upon different mechanisms of structural rearrangement. This free surface equilibration mechanism explains the success of the RTS principle and provides guidance regarding the types of order most readily enhanced by vapor deposition. This work extends the applicability of RTS to include molecular systems with a diverse range of higher-order liquid crystalline morphologies that could be useful for new organic electronic applications.

cond-mat.soft↗

arXiv2024

Resonant soft X-ray scattering reveals hierarchical structure in a multi-component vapor-deposited glass

Multi-phase vapor-deposited glasses are an important class of materials for organic electronics, particularly organic photovoltaics and thermoelectrics. These blends are frequently regarded as molecular alloys and there have been few studies of their structure at nanometer scales. Here we show that a co-deposited system of TPD and Disperse Orange 37, two small molecule glass-formers, separates into compositionally distinct phases with a domain size and spacing that depends on substrate temperature during deposition. Domains rich in one of the two components become larger and more pure at higher deposition temperatures. We use resonant soft X-ray scattering (RSoXS) complemented with Atomic Force Microscopy (AFM) and photo-induced force microscopy (PiFM) to measure the phase separation, topography, and purity of the deposited films. A forward-simulation approach to RSoXS analysis, the National Institute of Standards and Technology (NIST) RSoXS Simulation Suite (NRSS), is used with models developed from AFM images to evaluate the energy dependence of scattering across multiple length scales and interpret the RSoXS with respect to structure within the films. We find that the RSoXS is sensitive to a hidden length scale of phase separation that is not apparent from the AFM characterization alone. We demonstrate that vacuum scattering, which is often ignored in RSoXS analysis, contributes significantly to the features and energy dependence of the RSoXS pattern, and then illustrate how to properly account for vacuum scattering to analyze films with significant roughness. We then use this analysis framework to understand structure development mechanisms that occur during vapor deposition of a TPD-DO37 co-deposited glass with results that outline paths to tune morphology in multi-component materials.

cond-mat.mtrl-sci↗

arXiv2021

Vapor deposition rate modifies anisotropic glassy structure of an anthracene-based organic semiconductor

We control the anisotropic molecular packing of vapor-deposited glasses of ABH113, a deuterated anthracene derivative with promise for future OLED materials, by changing the deposition rate and substrate temperature at which they are prepared. We find that, at substrate temperatures from 0.65Tg to 0.92Tg, deposition rate significantly modifies the orientational order in the vapor-deposited glasses as characterized by X-ray scattering and birefringence. Both measures of anisotropic order can be described by a single deposition rate-substrate temperature superposition (RTS). This supports the applicability of the surface equilibration mechanism and generalizes the RTS principle from previous model systems with liquid crystalline order to non-mesogenic organic semiconductors. We find that vapor-deposited glasses of ABH113 have significantly enhanced density and thermal stability compared to their counterparts prepared by liquid-cooling. For organic semiconductors, the results of this study provide an efficient guide for using deposition rate to prepare stable glasses with controlled molecular packing.

cond-mat.mtrl-sci↗