# Direct Measurement of Density for Evaporated Thin Films

## TL;DR

A new method measures the density of thin films accurately using profilometry, microscopy, and high-vacuum TGA, avoiding assumptions about crystallinity.

## Contribution

The paper introduces a direct density measurement method that avoids assumptions about crystallinity or bulk properties.

## Key findings

- The method provides true density values for vapor-deposited thin films using high-vacuum TGA, profilometry, and microscopy.
- Density measurements are demonstrated for OLED, OPV, and OTFT materials and compared to other methods.
- The technique is applicable to a wide range of vacuum-stable thin film materials.

## Abstract

A simple and elegant method is reported for direct measurement of the density of vapor‐deposited thin films using a combination of profilometry, microscopy, and high‐vacuum thermogravimetric analysis (TGA). Density affects fabrication control, optical properties, charge transport, and mechanical properties of thin film devices. Accurate density determination is essential for optimizing device design to ensure film stability, charge balance, and light‐matter interactions. Exact mass of the vapor‐deposited thin films with suitable mass and aspect ratio is determined by high‐vacuum TGA. Combined with precise measurements of thickness and area for each film, the true density of individual films is captured as deposited. This method avoids common universalizing assumptions about the degree of crystallinity in a film. Furthermore, this method does not depend on bulk optical or electrical parameters that may vary as a result of the unique nanoscale properties of thin films. Density values are reported for a range of small molecule semiconductors commonly found in organic electronics such as organic light emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic thin film transistors (OTFTs), and compared to values calculated by other means. It is anticipated that this technique can be used to measure the density of a wide range of vacuum‐stable thin film materials.

We present a simple, direct method to measure the true density of vapor‐deposited thin films using profilometry, microscopy, and high‐vacuum TGA. Unlike conventional approaches, it avoids assumptions about crystallinity or bulk properties. Demonstrated across OLED, OPV, and OTFT materials, this technique provides accurate density values critical for optimizing film stability, charge transport, and light–matter interactions.