ISAJ Newsletter - Volume 7, Issue 1 (August 2022)

From the Editor’s Desk

Greetings and a warm welcome to the first issue of ISAJ Newsletter in 2022!

In this issue, we present you with three research articles and event report on 12th Annual ISAJ Symposium-2021. The research articles are on the study on Gallium oxide nanowires and its prospects for power devices and the futuristic possibility of integrating electricity generation from renewable sources and converting biomass-based carbon sources for energy and fine chemicals.

ISAJ organized its 12th Annual Symposium on November 26 (Fri) and 27 (Sat), 2021, which was jointly organized with the School of Marine Science and Technology, Tokai University at Shimizu-Ku of Shizuoka City in hybrid mode. The symposium was held in the Marine Science Museum Auditorium of the university situated at a picturesque viewpoint giving the best known view of Mt. Fuji.

Research Spotlight: Gallium Oxide and Its Future – A Review

By Dr. D. Arun Kumar, Nagoya University

Introduction

In the rapid development of electric power, industrial control, consumer electronics and automotive electronics industries, there is an ever-growing requirement for high performance power semiconductor devices. Such materials should be abundant, inexpensive, easy to fabricate, and have high thermal and chemical stability.

Compared to conventional Si and later developed SiC and GaN, recently developed gallium oxide (Ga₂O₃) has attracted much interest for high power device applications due to:

• Ultra-wide bandgap: 4.8 eV
• High breakdown field: Up to 8 MV/cm
• Baliga’s figure of merit: 3888 (10x SiC, 4x GaN)

Crystal Structure of β-Ga₂O₃

Among five structures of Ga₂O₃ single crystal, monoclinic β-phase is the most stable. β-Ga₂O₃ crystal has unique properties:

• Large lattice constant of 12.23 Å along [100] direction
• C2/m space group with base-centered arrangement
• Two different Ga atoms [Ga(I) and Ga(II)]
• Three different O atoms [O(I), O(II) and O(III)]

Electrical Properties

Energy Bandgap: β-Ga₂O₃ has an indirect bandgap of 4.83 eV, marginally less than direct bandgap of 4.87 eV. Due to weakness of indirect transitions, it effectively behaves as a direct bandgap material.

Dopants:

• N-type: Si, Ge, Sn, F, and Cl act as shallow donors
• P-type: Mg, Cu, Zn and N are potential dopants (challenging)

Synthesis Techniques

Multiple growth methods available:

• Molecular beam epitaxy (MBE)
• Metalorganic chemical vapor deposition (MOCVD)
• Pulsed laser deposition
• Hydrothermal method
• Thermal evaporation

MBE Growth Innovation

Recent breakthrough: Growth rate increased by more than 10 times by changing from (100) plane to (010) or (310) plane orientation.

Applications

Ga₂O₃ nanowires find applications in:

• Field-effect transistors (FETs)
• Temperature/gas sensors (high sensitivity due to surface-to-volume ratio)
• UV photodetectors (photoconductors, MSM photodiodes, Schottky diodes)
• Power devices

Challenges & Future Perspectives

1. Understanding factors affecting growth and properties
2. Addressing lattice mismatch issues
3. Improving ohmic and Schottky contacts
4. Enhancing carrier mobility
5. Reducing production costs for large-scale manufacturing

Conclusion

The wide bandgap of Ga₂O₃ makes it more sensitive to UV light than GaN and SiC and enables higher power device applications. Ga₂O₃ nanowires are expected to play a key role in next-generation power devices and sensors.

From the Pen of Young Mind: Catalytic Efficacy of Ni-Cu-Al Hydrotalcite Catalysts

By Upender Rao Thuppati, Nagoya University

Introduction

The sustainable energy sector explores renewable resources for energy and chemicals production to combat climate change and fossil fuel depletion. Biomass represents an abundant resource resembling fossil feedstocks. The integration of renewable electricity with biomass conversion offers promising pathways for sustainable chemical production.

Research Focus

This work compares thermal catalytic hydrogenation (TCH) and electrocatalytic hydrogenation (ECH) of furfural using Ni-Cu-Al hydrotalcite catalysts. Furfural, derived from acid-catalyzed hemicellulose reaction, serves as a platform chemical for synthetic chemicals and liquid fuels.

Catalyst Design Rationale

• Cu: Excellent affinity for furfural conversion to furfuryl alcohol (FAL)
• Ni: Remarkable selectivity towards tetrahydrofurfuryl alcohol (THFA)
• Combined: Complete conversion with enhanced selectivity

Catalyst Preparation

Three hydrotalcite catalysts prepared by co-precipitation:

1. Ni-Al₂O₃ HT
2. Cu-Al₂O₃ HT
3. Ni-Cu-Al₂O₃ HT

Metal to Al molar ratio: 2:1 Calcination/reduction: 500°C in air and 5% H₂/N₂

Results

Thermal Catalytic Hydrogenation (130°C, 20 bar H₂, 3 hours):

• Ni-Al₂O₃ HT: 42% furfural conversion
• Cu-Al₂O₃ HT: 82% conversion
• Ni-Cu-Al₂O₃ HT: 100% conversion, 93% FAL yield
• Physical mixing of Ni+Cu: 47% THFA yield

Electrocatalytic Hydrogenation:

• All catalysts active for FAL and 2-methylfuran formation
• Hydrogen evolution reaction (HER) dominant
• Further optimization needed for improved faradaic efficiency

Advantages of ECH

1. Simple operating conditions
2. No external H₂ source required
3. Cleaner process
4. Easy product separation
5. Higher carbon recovery

Conclusion

Ni-Cu-Al mixed oxide hydrotalcite catalysts show superior activity for TCH of furfural at moderate conditions. Future work focuses on optimizing ECH conditions to maximize THFA yields, advancing sustainable chemical production from biomass.

Event Report: 12th ISAJ Annual Symposium 2021

The 12th ISAJ Annual Symposium on “Science-Technology-Innovation (STI) Towards a Sustainable World” was held November 26-27, 2021, at Tokai University, Shimizu campus, Shizuoka, in hybrid format.

Special Celebrations

• First year of UN Decade of Ocean Science for Sustainable Development (2021-2030)
• 70 years of India-Japan diplomatic relations

Opening Ceremony

• Welcome: Prof. Hiroshi Saito, Dean, School of Marine Science and Technology
• Inauguration: H.E. Mr. Sanjay Kumar Verma, Ambassador of India to Japan
• Special Messages: Prof. Kiyoshi Yamada (Chancellor, Tokai University) and Mr. Nobuhiro Tanabe (Mayor, Shizuoka City)
• Keynote: Prof. Asahiko Taira, Ex-President JAMSTEC

Awards Presented

ISAJ Lifetime Achievement Award: Dr. Renu Wadhwa, AIST Tsukuba

Distinguished Mentor Award: Dr. Toshio Yamagata, formerly JAMSTEC

Program Highlights

Day 1: Ocean Science and Technology focus

• Multiple plenary and invited talks by senior scientists

Day 2: Diverse research presentations

• Biology and medicine
• Power and structural engineering
• Energy and environment
• Material science and physical sciences

Participation

• 65 total talks (largest in 12-year history)
• 100 participants from Japan and internationally (India, South Korea, Indonesia, Germany)
• Hybrid format: Both in-person and virtual presentations
• One-third presented in person

Unique Venue

Marine Science Museum Auditorium offered:

• Spectacular coastal views
• Best known view of Mt. Fuji
• Visit to JAMSTEC’s deep-sea drilling ship Chikyu

Impact

The hybrid format attracted overwhelming response with the largest number of abstracts in symposium history, successfully adapting to post-pandemic research collaboration needs while celebrating major milestones in India-Japan relations and ocean science.