Engineering topics

Bulovic, Vladimir

Publications and source records attributed to Bulovic, Vladimir.

3 records

DOE OSTI2023

Influence of Codeposition on Methylammonium Iodide Degradation during Vapor Transport Deposition

Vapor transport deposition (VTD) is one manufacturing-compatible technique for large-scale deposition of perovskite films. However, to date, little understanding has been given to degradation products formed by perovskites grown under vacuum. Here, we use methylammonium iodide (MAI) as an example organic precursor to identify degradation patterns through both the sublimation process and transport through a zone with temperatures much higher than MAI can thermodynamically survive. We show that degradation due to sublimation effects MAI powders and subsequent integration into methylammonium lead iodide (MAPbI3) films differently than degradation solely due to material transport through a very high-temperature zone. Additionally, we categorize common post-deposition treatments by their influence on the degradation products seen in MAPbI3 films. Furthermore, with these results we give recommendations for VTD reactor design and the feasibility of co-deposition as a film growth technique.

14 SOLAR ENERGY↗

DOE OSTI2023

Vertical full-colour micro-LEDs via 2D materials-based layer transfer

Micro-LEDs (µLEDs) have been explored for augmented and virtual reality display applications that require extremely high pixels per inch and luminance. However, conventional manufacturing processes based on the lateral assembly of red, green and blue (RGB) µLEDs have limitations in enhancing pixel density. Recent demonstrations of vertical µLED displays have attempted to address this issue by stacking freestanding RGB LED membranes and fabricating top-down, but minimization of the lateral dimensions of stacked µLEDs has been difficult. Here we report full-colour, vertically stacked µLEDs that achieve, to our knowledge, the highest array density (5,100 pixels per inch) and the smallest size (4 µm) reported to date. This is enabled by a two-dimensional materials-based layer transfer technique that allows the growth of RGB LEDs of near-submicron thickness on two-dimensional material-coated substrates via remote or van der Waals epitaxy, mechanical release and stacking of LEDs, followed by top-down fabrication. The smallest-ever stack height of around 9 µm is the key enabler for record high µLED array density. We also demonstrate vertical integration of blue µLEDs with silicon membrane transistors for active matrix operation. Furthermore, these results establish routes to creating full-colour µLED displays for augmented and virtual reality, while also offering a generalizable platform for broader classes of three-dimensional integrated devices.

42 ENGINEERING↗

NASA NTRS2012

Organic materials able to detect analytes

The present invention generally relates to polymers with lasing characteristics that allow the polymers to be useful in detecting analytes. In one aspect, the polymer, upon an interaction with an analyte, may exhibit a change in a lasing characteristic that can be determined in some fashion. For example, interaction of an analyte with the polymer may affect the ability of the polymer to reach an excited state that allows stimulated emission of photons to occur, which may be determined, thereby determining the analyte. In another aspect, the polymer, upon interaction with an analyte, may exhibit a change in stimulated emission that is at least 10 times greater with respect to a change in the spontaneous emission of the polymer upon interaction with the analyte. The polymer may be a conjugated polymer in some cases. In one set of embodiments, the polymer includes one or more hydrocarbon side chains, which may be parallel to the polymer backbone in some instances. In another set of embodiments, the polymer may include one or more pendant aromatic rings. In yet another set of embodiments, the polymer may be substantially encapsulated in a hydrocarbon. In still another set of embodiments, the polymer may be substantially resistant to photobleaching. In certain aspects, the polymer may be useful in the detection of explosive agents, such as 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT).

Rose, Aimee↗