Fabrication and micro-Raman spectroscopy of arrays of copper phthalocyanine molecular-magnet microdisks

TL;DR

This paper presents a top-down fabrication method for creating ordered arrays of copper phthalocyanine microdisks and analyzes their structural and vibrational properties using micro-Raman spectroscopy, revealing a stable crystalline phase.

Contribution

It introduces a novel lithography-based fabrication approach for CuPc microstructures and provides detailed spectroscopic characterization of their phase and thermal stability.

Findings

CuPc microdisks have 5 μm diameter and 7-70 nm height.

Micro-Raman spectra show a stable β crystalline phase.

Laser heating causes peak shifts indicating thermal stability.

Abstract

Phthalocyanines as organic semiconductors and molecular magnets provide plenty of industrial or high-tech applications from dyes and pigments up to gas sensors, molecular electronics, spintronics and quantum computing. Copper phthalocyanine (CuPc) belongs among the most used phthalocyanines, typically in the form of powder or films but self-grown nanowires are also known. Here we describe an opposite, i.e., top-down approach based on fabrication of ordered arrays of CuPc microstructures (microdisks) using electron beam lithography and other steps. Among critical points of this approach belongs a choice of a proper resist and a solvent. Fabricated CuPc microdisks have a diameter of 5 ${\mu}$m and heights from 7 up to 70 nm. Micro-Raman spectroscopy of the films and microdisks reveals a crystalline ${\beta}$ phase associated with a paramagnetic form. Additional measurements with an increasing laser power show a significant shift (${\Delta}{\omega}$ ~ 7.1 cm$^{-1}$ ) and broadening of a peak at 1532 rel$\cdot$cm$^{-1}$ corresponding to the phonon B1g mode. The observed smooth changes exclude a phase transition and confirm the thermally stable polymorph. Our versatile fabrication technique using the common lithographic resist brings new possibilities for the fabrication of various micro/nanostructures such as micromagnets, heterostructures or organic electronic devices.