Transforming nickel crystals under heat and solvent exposure.

Crystal Clear: How Scientists Are Tuning Semiconductor Performance with Nickel

Soraya Malik in Tech & Innovation August 2025 • 4 min read.

"Unlocking new potential in semiconductor technology through innovative crystal transformation techniques in nickel complexes."

Imagine a world where our electronic devices are not only more powerful but also more adaptable, thanks to advancements at the molecular level. Polymorphism, the ability of a solid material to exist in multiple crystal forms, is a phenomenon that has long intrigued scientists. These different forms can exhibit a range of properties, from color and solubility to magnetic and electrical behaviors. Recent studies have focused on how to harness this variability, particularly in metal-organic hybrid crystals, to revolutionize semiconductor technology.

Semiconductors are the backbone of modern electronics, found in everything from smartphones to solar panels. Traditionally, research has centered on organic oligomers and polymers. However, the spotlight is now turning to coordination complexes—structures where a central metal atom is surrounded by ligands (molecules or ions)—offering new avenues for creating superior semiconductor materials. These complexes, especially those with planar, conjugated ligands, have shown promise in enhancing the performance of organic field-effect transistors (OFETs), light-emitting diodes (LEDs), and photovoltaic devices (PVs).

One particularly promising area involves Schiff bases, conjugated compounds known for their interesting optoelectronic properties. When used as semiconductor materials and combined with the concept of crystal transformation, these bases could lead to significant advancements. The key is understanding how altering the crystal structure of these materials can fine-tune their semiconducting properties, opening up possibilities for new and improved modification methods.

Tuning Nickel Complexes Through Crystal Transformation

Transforming nickel crystals under heat and solvent exposure.

A groundbreaking study has explored the crystal transformation between two polymorphs of a square-planar nickel complex, known as NiL2. The two forms are a green crystal (1-G) and a red crystal (1-R). NiL2 (L = 2-ethoxy-6-(N-methyliminomethyl)phenolate) and its tuning effect on semiconductor properties were meticulously examined both experimentally and theoretically. The transformation occurs when 1-G is heated to 413 K (approximately 140°C), converting it to 1-R. Conversely, soaking 1-R in various solvents reverts it back to the 1-G form. This reversible transformation offers a unique way to manipulate the material's properties.

Crystallographic and powder X-ray diffraction (PXRD) studies revealed significant changes in crystal dimensions resulting from alterations in packing models. The electrical conductivity of a device made from 1-G (D-1-G(298)) dramatically increases when heated to 413 K, jumping from 6.55 × 10⁻⁴ S/cm to 1.11 × 10⁻³ S/cm. This demonstrates a significant crystal form dependence, where the heat-treating of D-1-G and D-1-R devices at different temperatures elucidates the reasons for conductivity tuning.

Heating 1-G: Converts it to 1-R at 413K.
Soaking 1-R: Reverts it back to 1-G in solvents.
Conductivity Increase: Significant increase upon heating 1-G.
Crystal Changes: Dramatic changes in crystal dimensions and packing models.

Theoretical calculations have illuminated the reasons behind these conductivity changes, predicting that both polymorphs are effective p-type semiconductors. The hole mobilities are 1.63 × 10⁻² cm²/Vs for 1-G and 2.11 × 10⁻¹ cm²/Vs for 1-R. These findings suggest that the conductivity of NiL2-based devices can be precisely tuned through crystal transformation, induced either by heating or solvent soaking.

The Future of Semiconductor Tuning

This research not only enhances our understanding of crystal transformations but also paves the way for designing new semiconductor materials with superior performance. By manipulating the crystal structure of nickel complexes, scientists can achieve precise control over their electrical properties, opening up exciting possibilities for more efficient and versatile electronic devices. This approach offers a promising avenue for future innovations in semiconductor technology, potentially leading to breakthroughs in various applications.

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This article is based on research published under:

DOI-LINK: 10.1021/acs.inorgchem.8b01841, Alternate LINK

Title: Tuning Semiconductor Performance Of Nickel Complexes Through Crystal Transformation

Subject: Inorganic Chemistry

Journal: Inorganic Chemistry

Publisher: American Chemical Society (ACS)

Authors: Yan-Fang Wu, Shuai Zhao, Hong-Xu Na, Pei-Yu Yang, Haibing Xu, Yuexing Zhang, Yanli Chen, Ming-Hua Zeng

Published: 2018-09-25

Everything You Need To Know

What does polymorphism mean in the context of metal-organic hybrid crystals and why is it important for semiconductor technology?

Polymorphism refers to the ability of a solid material, like the nickel complex NiL2, to exist in multiple crystal forms. Each of these forms can have different properties, such as color, solubility, magnetic behavior, and electrical conductivity. Understanding and manipulating polymorphism allows scientists to fine-tune the properties of semiconductors for specific applications. This is particularly relevant in metal-organic hybrid crystals, where different crystal forms can drastically alter the semiconducting behavior.

What are Schiff bases, and how do they contribute to advancements in semiconductor materials, particularly when combined with crystal transformation techniques?

Schiff bases are conjugated compounds with interesting optoelectronic properties that show promise as semiconductor materials. When combined with the concept of crystal transformation, Schiff bases like those found in the nickel complex NiL2, can be used to create advanced semiconductor devices. By altering the crystal structure of Schiff bases, we can fine-tune their semiconducting properties, leading to new and improved modification methods. This makes them highly valuable in the creation of organic field-effect transistors (OFETs), light-emitting diodes (LEDs), and photovoltaic devices (PVs).

How can the crystal transformation between the green (1-G) and red (1-R) forms of the nickel complex NiL2 be induced, and why is this reversible transformation significant?

The crystal transformation between the green crystal form (1-G) and the red crystal form (1-R) of the nickel complex NiL2 can be induced by heating or solvent soaking. Heating 1-G to 413 K (approximately 140°C) converts it to 1-R, while soaking 1-R in various solvents reverts it back to the 1-G form. This reversible transformation is significant because it allows scientists to manipulate the material's electrical conductivity. For instance, the electrical conductivity of a device made from 1-G dramatically increases when heated to convert it to 1-R.

What do theoretical calculations reveal about the electrical properties of the green (1-G) and red (1-R) polymorphs of the nickel complex NiL2, and what are the implications?

Theoretical calculations suggest that both the green crystal (1-G) and red crystal (1-R) polymorphs of the nickel complex NiL2 are effective p-type semiconductors, meaning they conduct electricity through the movement of positive charges (holes). The hole mobility, which indicates how easily these holes move through the material, is 1.63 × 10⁻² cm²/Vs for 1-G and 2.11 × 10⁻¹ cm²/Vs for 1-R. The implication is that the conductivity of NiL2-based devices can be precisely tuned through crystal transformation, affecting their performance in electronic applications. Further theoretical exploration could reveal additional properties to tune.

How does the ability to tune semiconductor performance through crystal transformation in nickel complexes like NiL2 potentially impact the future of electronic devices and applications?

The ability to tune semiconductor performance through crystal transformation in nickel complexes like NiL2 opens up possibilities for creating more efficient and versatile electronic devices. By manipulating the crystal structure of these materials, scientists can achieve precise control over their electrical properties. This could lead to breakthroughs in organic field-effect transistors (OFETs), light-emitting diodes (LEDs), and photovoltaic devices (PVs). The potential applications span from more powerful smartphones to more efficient solar panels. Further research could lead to new materials and methods for semiconductor design.