A research team led by Tohoku University announced on November 12 that it had built a prototype transistor using cellulose nanofibers modified with phosphate-derived functional groups, and confirmed that irradiating it with green light reduces its current. The team verified the electrical response through light irradiation and current measurements, and investigated the mechanism behind it by combining electron spin resonance measurements with first-principles calculations.
Participants in the study included Mikio Fukuhara and Takahito Ono of Tohoku University, Nobuhisa Fujima of Shizuoka University, and Oji Holdings. According to Tohoku University, the paper was published on November 4, 2026, in the peer-reviewed journal AIP Advances. The paper's DOI is 10.1063/5.0353127.
A Prototype Transistor Made From Processed Cellulose Nanofibers
The team used phosphate-esterified amorphous cellulose nanofibers (APCNF). Phosphate esterification is a chemical treatment that introduces phosphate-derived functional groups into cellulose. "Amorphous" means the atomic arrangement lacks the regularity of a crystal. The fibers used in this study had a diameter of 4.46 nm.
The prototype transistor has a three-terminal structure: APCNF is placed between aluminum source and drain electrodes, with a gold gate electrode in contact with it. It is a metal-semiconductor field-effect transistor (MESFET), which uses a metal-semiconductor Schottky junction to control current through the gate voltage. Light was applied from the underside of the device.
The team also measured the optical properties of APCNF separately. For a 1 μm-thick APCNF sheet, light transmittance was 0.90 at a wavelength of 400 nm and 0.92 at 800 nm, with refractive indices of 1.58 and 1.52, respectively. These measurements indicate high transparency, but they do not represent the transmittance of the entire transistor, including its electrodes.
Current Drops Under Green Light at 490–550 nm
In the light irradiation tests, the team measured drain current across wavelengths from 350 to 800 nm while varying the gate voltage from −5 V to +5 V. The drain current dropped significantly under green light in the range of roughly 490–550 nm.
Separately, in the transfer characteristics, which show the relationship between gate voltage and drain current, a current of 2.09 mA was obtained at a drain voltage of 1.0 V and a gate voltage of 4.1 V. This 2.09 mA is a transfer-characteristic measurement and does not indicate how much the current changed before and after green light irradiation.
Investigating the Mechanism With Electron Spin Resonance and First-Principles Calculations
While experiments confirmed that green light reduces the current, explaining the cause at the atomic level requires a detailed look at the electronic states. The team combined electron spin resonance, which detects unpaired electrons, with first-principles calculations, which theoretically examine the behavior of atoms and electrons, to study how the current changes.
Based on Tohoku University's release, the measurement results, computational estimates, and application concepts from this study can be summarized as follows.
| Method and target | Result | Status of the result |
|---|---|---|
| Light irradiation and current measurement of the prototype MESFET | Drain current decreased at around 490–550 nm | Electrical response observed in light irradiation tests |
| Electron spin resonance measurement | Signal detected at a g-value of 2.0052 | Measurement result the team attributed to oxygen-derived radicals |
| First-principles calculations | Radicals estimated to localize preferentially on oxygen atoms in phosphate ester bonds | Theoretical explanation of radical location |
| Application concepts presented by the university | Devices integrated with windows or displays, biosensors, etc. | Outlook for future applications |
From the signal detected in the electron spin resonance measurement, the team concluded that oxygen-derived radicals are present. A radical is an atom or molecule with an unpaired electron. First-principles calculations then suggested that this unpaired electron localizes preferentially on oxygen atoms in the phosphate ester bonds. The electron spin resonance measurement result and the computational estimate of the radical's specific location need to be distinguished.
The team believes that green light irradiation causes free electrons to be lost, widening the depletion layer, a region with few electrons to carry current, and thereby reducing the drain current. This is an interpretation of the mechanism based on measurements and calculations, not a direct observation of how the electronic state of each atom changes under illumination.
Applications in Transparent Electronics and the Challenge of Mass Production
The team also measured the electrical properties of APCNF. The electron mobility, determined from the Hall coefficient, was 16.33 cm²/(V·s), indicating how easily electrons move through the material. Measurement with a photoelectron yield spectrometer in air gave a work function of 5.31 eV. The work function represents the energy required to extract an electron from inside a substance to the outside. Both are indicators for evaluating the material's electrical properties and do not directly show the device's power consumption or switching speed.
The university's release does not give details on the number of devices fabricated, how many times measurements were repeated, or the variability of results. It also does not state the light irradiation intensity, the temperature and humidity during measurement, the measured response time of optical switching, or the settings used in the first-principles calculations, such as the computational cell and functional. A search using the paper's title and DOI also found no published independent replication of this research.
Tohoku University has outlined plans to apply the results to optoelectronic convergence technology that combines optical and electrical signals, and to use the material's transparency in information terminals integrated with windows or displays, as well as biosensors. As a manufacturing challenge for practical use, it cited the need to establish a mass-production process that treats APCNF uniformly over large areas. Whether different samples show the same optical response, how quickly the device responds to switching light on and off, and whether uniform electrical properties can be maintained over large areas will be important in judging specific applications.