Okayama University


Okayama University Medical Research Updates (OU-MRU) Vol.103

September 09, 2022

Source: Okayama University (JAPAN), Public Relations Division
For immediate release: 9 September 2022
Okayama University research: High-quality growth

(Okayama, 9 September) Researchers at Okayama University report in ACS Nano how highly crystalline samples of transition metal dichalcogenides such as MoS2 and WS2 can be grown. These ultra-thin and mechanically flexible materials are important for the development of flexible optoelectronic device applications.

Transition metal dichalcogenides (TMDCs) are a class of materials with physical properties that make them ideally suited for use in flexible optoelectronic applications, such as light detectors, light-emitting diodes and solar cells. For such applications to perform well, the crystalline quality of the TMDCs needs to be extremely high, however; defects in the crystal structure worsen device performance. The crystalline quality of a sample is related to the number of grain boundaries — interfaces between different grains, or domains, within the crystal. Different domains have the same chemical composition and structure but are oriented differently with respect to each other. The lower the number of grain boundaries, the larger the domains, and the better the sample’s crystallinity. Now, Assistant Professor SUZUKI Hiroo and HASHIMOTO Ryoki (graduate students) Okayama University and colleagues have developed a technique with which highly crystalline TMDCs can be grown. Furthermore, the technique enables to optimize the performance of TMDCs for optoelectronic devices.

The researchers’ approach is based on chemical vapor deposition (CVD), a method in which a substrate is put in a vacuum chamber and is exposed to particular chemical vapors. This leads to chemical reactions and depositions on the substrate, resulting in the growth of the desired material. Assistant Professor SUZUKI and colleagues grew the TMDCs MoS2 (molybdenum disulfide) and WS2 (tungsten disulfide), for which they let metal salts and sulfur sources react in the CVD chamber. What was special is that they used a stacked substrate configuration: two silicon-based substrates put close to each other, creating a confined environment for the TMDCs to form. This type of ‘microreactor’ led to the growth of samples with large domains.

Through careful analysis of the obtained crystals’ morphology and numerical modelling of the processes at play, Assistant Professor SUZUKI and colleagues deduced that the growth is governed by surface diffusion, that is, by atoms moving along the substrate surface. This leads to a lower probability for atoms to nucleate and initiate the growth of a domain; instead of several small domains, only one or a few large domains develop.

The scientists then investigated how the growth temperature used in the CVD process influenced the materials’ photoluminescence — the ability to emit light of a particular wavelength after being irradiated with light of another wavelength. They found that for a growth temperature of about 820°C, the photoluminescence characteristics of WS2 are optimal.

In conclusion, the reported growth method produces, in a controlled way, highly crystalline TMDC samples that are suitable for use in optoelectronic applications. Quoting the researchers: “These findings should significantly contribute to the realization of applications of high-performance optoelectronic devices based on high-quality monolayer TMDCs.”

Chemical vapor deposition

In chemical vapor deposition (CVD), one or more gases are made to pass over a hot substrate’s surface under (low) vacuum. The gases dissociate on the substrate or in its immediate vicinity, after which the decomposition products accumulate on the surface. Often, by-products are formed in the process; these are removed from the reaction chamber through gas flow.

By choosing the gases that are injected into the CVD chamber, specific materials can be grown. Various types of materials structures can be obtained, including monocrystalline (consisting of one domain only), polycrystalline (consisting of several domains) or amorphous materials.
Assistant Professor SUZUKI Hiroo and HASHIMOTO Ryoki from Okayama University and colleagues have now used a CVD approach to grow highly crystalline samples of transition metal dichalcogenides, specifically MoS2 and WS2, by using a stacked substrate setup; the resulting confinement provides optimal conditions for monocrystals to grow.

Hiroo Suzuki, Ryoki Hashimoto, Masaaki Misawa, Yijun Liu, Misaki Kishibuchi, Kentaro Ishimura, Kenji Tsuruta, Yasumitsu Miyata, and Yasuhiko Hayashi. Surface Diffusion-Limited Growth of Large and High-Quality Monolayer Transition Metal Dichalcogenides in Confined Space of Microreactor. ACS Nano, 2022, 16, 11360−11373.

Correspondence to
Assistant Professor SUZUKI Hiroo, Ph.D.
Nanodevice and Materials Engineering laboratory,
Graduate School of Natural Science and Technology,
Okayama University, 3-1-1 Tsushima-naka, Kita-ku,
Okayama 700-8530, Japan
E-mail: hiroo.suzuki (a) okayama-u.ac.jp
For inquiries, please contact us by replacing (a) with the @

Further information
Okayama University
1-1-1 Tsushima-naka , Kita-ku , Okayama 700-8530, Japan
Public Relations Division
E-mail: www-adm(a) adm.okayama-u.ac.jp
For inquiries, please contact us by replacing (a) with the @ mark.
Website: //www.okayama-u.ac.jp/index_e.html
Okayama Univ. e-Bulletin: //www.okayama-u.ac.jp/user/kouhou/ebulletin/
We love OKAYAMA UNIVERSITY: https://www.youtube.com/watch?v=7cXlttQIk3E
Okayama University Image Movie(2020)
Okayama University supports the Sustainable Development Goals: https://sdgs.okayama-u.ac.jp/en/

Okayama University Medical Research Updates (OU-MRU)
The whole volume : OU-MRU (1- )
Vol.1:Innovative non-invasive ‘liquid biopsy’ method to capture circulating tumor cells from blood samples for genetic testing
Vol.2:Ensuring a cool recovery from cardiac arrest
Vol.3:Organ regeneration research leaps forward
Vol.4:Cardiac mechanosensitive integrator
Vol.5:Cell injections get to the heart of congenital defects
Vol.6:Fourth key molecule identified in bone development
Vol.7:Anticancer virus solution provides an alternative to surgery
Vol.8:Light-responsive dye stimulates sight in genetically blind patients
Vol.9:Diabetes drug helps towards immunity against cancer
Vol.10:Enzyme-inhibitors treat drug-resistant epilepsy
Vol.11:Compound-protein combination shows promise for arthritis treatment
Vol.12:Molecular features of the circadian clock system in fruit flies
Vol.13:Peptide directs artificial tissue growth
Vol.14:Simplified boron compound may treat brain tumours
Vol.15:Metamaterial absorbers for infrared inspection technologies
Vol.16:Epigenetics research traces how crickets restore lost limbs
Vol.17:Cell research shows pathway for suppressing hepatitis B virus
Vol.18:Therapeutic protein targets liver disease
Vol.19:Study links signalling protein to osteoarthritis
Vol.20:Lack of enzyme promotes fatty liver disease in thin patients
Vol.21:Combined gene transduction and light therapy targets gastric cancer
Vol.22:Medical supportive device for hemodialysis catheter puncture
Vol.23:Development of low cost oral inactivated vaccines for dysentery
Vol.24:Sticky molecules to tackle obesity and diabetes
Vol.25:Self-administered aroma foot massage may reduce symptoms of anxiety
Vol.26:Protein for preventing heart failure
Vol.27:Keeping cells in shape to fight sepsis
Vol.28:Viral-based therapy for bone cancer
Vol.29:Photoreactive compound allows protein synthesis control with light
Vol.30:Cancer stem cells’ role in tumor growth revealed
Vol.31:Prevention of RNA virus replication
Vol.32:Enzyme target for slowing bladder cancer invasion
Vol.33:Attacking tumors from the inside
Vol.34:Novel mouse model for studying pancreatic cancer
Vol.35:Potential cause of Lafora disease revealed
Vol.36:Overloading of protein localization triggers cellular defects
Vol.37:Protein dosage compensation mechanism unravelled
Vol.38:Bioengineered tooth restoration in a large mammal
Vol.39:Successful test of retinal prosthesis implanted in rats
Vol.40:Antibodies prolong seizure latency in epileptic mice
Vol.41:Inorganic biomaterials for soft-tissue adhesion
Vol.42:Potential drug for treating chronic pain with few side effects
Vol.43:Potential origin of cancer-associated cells revealed
Vol.44:Protection from plant extracts
Vol.45:Link between biological-clock disturbance and brain dysfunction uncovered
Vol.46:New method for suppressing lung cancer oncogene
Vol.47:Candidate genes for eye misalignment identified
Vol.48:Nanotechnology-based approach to cancer virotherapy
Vol.49:Cell membrane as material for bone formation
Vol.50:Iron removal as a potential cancer therapy
Vol.51:Potential of 3D nanoenvironments for experimental cancer
Vol.52:A protein found on the surface of cells plays an integral role in tumor growth and sustenance
Vol.53:Successful implantation and testing of retinal prosthesis in monkey eyes with retinal degeneration
Vol.54:Measuring ion concentration in solutions for clinical and environmental research
Vol.55:Diabetic kidney disease: new biomarkers improve the prediction of the renal prognosis
Vol.56:New device for assisting accurate hemodialysis catheter placement
Vol.57:Possible link between excess chewing muscle activity and dental disease
Vol.58:Insights into mechanisms governing the resistance to the anti-cancer medication cetuximab
Vol.59:Role of commensal flora in periodontal immune response investigated
Vol.60:Role of commensal microbiota in bone remodeling
Vol.61:Mechanical stress affects normal bone development
Vol.62:3D tissue model offers insights into treating pancreatic cancer
Vol.63:Promising biomarker for vascular disease relapse revealed
Vol.64:Inflammation in the brain enhances the side-effects of hypnotic medication
Vol.65:Game changer: How do bacteria play Tag ?
Vol.66:Is too much protein a bad thing?
Vol.67:Technology to rapidly detect cancer markers for cancer diagnosis
Vol.68:Improving the diagnosis of pancreatic cancer
Vol.69:Early gastric cancer endoscopic diagnosis system using artificial intelligence
Vol.70:Prosthetics for Retinal Stimulation
Vol.71:The nervous system can contribute to breast cancer progression
Vol.72:Synthetic compound provides fast screening for potential drugs
Vol.73:Primary intraocular lymphoma does not always spread to the central nervous system
Vol.74:Rising from the ashes—dead brain cells can be regenerated after traumatic injury
Vol.75:More than just daily supplements — herbal medicines can treat stomach disorders
Vol.76:The molecular pathogenesis of muscular dystrophy-associated cardiomyopathy
Vol.77:Green leafy vegetables contain a compound which can fight cancer cells
Vol.78:Disrupting blood supply to tumors as a new strategy to treat oral cancer
Vol.79:Novel blood-based markers to detect Alzheimer’s disease
Vol.80:A novel 3D cell culture model sheds light on the mechanisms driving fibrosis in pancreatic cancer
Vol.81:Innovative method for determining carcinogenicity of chemicals using iPS cells
Vol.82:Making memories — the workings of a neuron revealed
Vol.83:Skipping a beat — a novel method to study heart attacks
Vol.84:Friend to Foe—When Harmless Bacteria Turn Toxic
Vol.85:Promising imaging method for the early detection of dental caries
Vol.86:Plates and belts — a toolkit to prevent accidental falls during invasive vascular proceduresa
Vol.87:Therapeutic potential of stem cells for treating neurodegenerative disease
Vol.88:Nanotechnology for making cancer drugs more accessible to the brain
Vol.89:Studying Parkinson’s disease with face-recognition software
Vol.90:High levels of television exposure affect visual acuity in children
Vol.91:Meeting high demand: Increasing the efficiency of antiviral drug production in bacteria
Vol.92:Numerical modelling to assist the development of a retinal prosthesis
Vol.93:Repurposing cancer drugs: An innovative therapeutic strategy to fight bone cancer
Vol.94:A berry vine found in Asia proves useful in combating lung cancer
Vol.95:A new avenue for detecting cancer in the blood
Vol.96:Automated cell image analysis
Vol.97:Artificial intelligence helps to determine cancer invasion
Vol.98:Okayama University launches clinical trials of a jawbone regeneration therapy using human BMP-2 transgenic protein derived from Escherichia coli.
Vol.99:A rapid flow process that can convert droplets into multilayer polymeric microcapsules
Vol.100:Understanding insect leg regeneration
Vol.101:Oral tumor progression mechanism identified
Vol.102:Controlled cell death by irradiation with light