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Featured researches published by D. Trainer.


Scientific Reports | 2017

Inter-Layer Coupling Induced Valence Band Edge Shift in Mono- to Few-Layer MoS 2

D. Trainer; A. Putilov; Cinzia Di Giorgio; Timo Saari; Baokai Wang; Mattheus Wolak; Ravini U. Chandrasena; Christopher Lane; Tay-Rong Chang; Horng-Tay Jeng; Hsin Lin; Florian Kronast; A. X. Gray; X. X. Xi; Jouko Nieminen; A. Bansil; M. Iavarone

Recent progress in the synthesis of monolayer MoS2, a two-dimensional direct band-gap semiconductor, is paving new pathways toward atomically thin electronics. Despite the large amount of literature, fundamental gaps remain in understanding electronic properties at the nanoscale. Here, we report a study of highly crystalline islands of MoS2 grown via a refined chemical vapor deposition synthesis technique. Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS), photoemission electron microscopy/spectroscopy (PEEM) and μ-ARPES we investigate the electronic properties of MoS2 as a function of the number of layers at the nanoscale and show in-depth how the band gap is affected by a shift of the valence band edge as a function of the layer number. Green’s function based electronic structure calculations were carried out in order to shed light on the mechanism underlying the observed bandgap reduction with increasing thickness, and the role of the interfacial Sulphur atoms is clarified. Our study, which gives new insight into the variation of electronic properties of MoS2 films with thickness bears directly on junction properties of MoS2, and thus impacts electronics application of MoS2.


Scientific Reports | 2018

Evolution of Metastable Defects and Its Effect on the Electronic Properties of MoS 2 Films

M. Precner; T. Polaković; Qiao Qiao; D. Trainer; A. Putilov; C. Giorgio; I. Cone; Y. Zhu; X. X. Xi; M. Iavarone; G. Karapetrov

We report on structural and electronic properties of defects in chemical vapor-deposited monolayer and few-layer MoS2 films. Scanning tunneling microscopy, Kelvin probe force microscopy, and transmission electron microscopy were used to obtain high resolution images and quantitative measurements of the local density of states, work function and nature of defects in MoS2 films. We track the evolution of defects that are formed under heating and electron beam irradiation. We observe formation of metastable domains with different work function values after annealing the material in ultra-high vacuum to moderate temperatures. We attribute these metastable values of the work function to evolution of crystal defects forming during the annealing. The experiments show that sulfur vacancies formed after exposure to elevated temperatures diffuse, coalesce, and migrate bringing the system from a metastable to equilibrium ground state. The process could be thermally or e-beam activated with estimated energy barrier for sulfur vacancy migration of 0.6 eV in single unit cell MoS2. Even at equilibrium conditions, the work function and local density of states values are strongly affected near grain boundaries and edges. The results provide initial estimates of the thermal budgets available for reliable fabrication of MoS2-based integrated electronics and indicate the importance of defect control and layer passivation.


Journal of Applied Physics | 2016

Graphene tunnel junctions with aluminum oxide barrier

Ying Feng; D. Trainer; Ke Chen

We report a development of graphene tunnel junctions made by chemical vapor deposition grown graphene and sputtered aluminum insulating by an in-situ grown aluminum oxide. The thin oxide layer formed in between the metal layer and the two-dimensional material is a crucial part of a tunnel junction. We characterized surface morphology of oxide layers and studied tunneling spectra of lead and silver tunnel junctions to estimate the quality of the aluminum oxide. The Brinkman-Rowell-Dynes model was applied to fit the conductance-voltage plots to calculate the thickness of oxide layers. Junctions with graphene both on bottom and on top were fabricated and their tunneling properties were characterized after exposure to air for weeks to test time stability. Furthermore, the resistances of graphene tunnel junctions with aluminum oxide formed naturally and in an oxygen atmosphere were studied. Our results demonstrate that in-situ aluminum oxide is an effective barrier for graphene tunnel junctions. The methods of...


Archive | 2018

Metastable defects in monolayer and few-layer films of MoS2

M. Precner; T. Polaković; D. Trainer; A. Putilov; C. Di Giorgio; I. Cone; X. X. Xi; M. Iavarone; G. Karapetrov

We report on structural and electronic properties of defects in chemical vapor-deposited monolayer and few-layer MoS2 films. We use scanning tunneling microscopy and Kelvin probe force microscopy in order to obtain measurements of the local density of states, work function and nature of defects in MoS2 films. We track the evolution of defects that are formed under annealing in ultra-high vacuum conditions. We observe formation of metastable domains with different work function values after annealing the material in ultra-high vacuum to moderate temperatures. We attribute these metastable values of the work function to evolution of crystal defects forming during the annealing. The experiments show that sulfur vacancies formed after exposure to elevated temperatures diffuse, coalesce, and migrate bringing the system from a metastable to equilibrium ground state. The process could be thermally activated with estimated energy barrier for sulfur vacancy migration of 0.6 eV in single unit cell MoS2. The results provide estimates of the thermal budgets available for reliable fabrication of MoS2-based integrated circuit electronics and indicate the importance of defect control and layer passivation.We report on structural and electronic properties of defects in chemical vapor-deposited monolayer and few-layer MoS2 films. We use scanning tunneling microscopy and Kelvin probe force microscopy in order to obtain measurements of the local density of states, work function and nature of defects in MoS2 films. We track the evolution of defects that are formed under annealing in ultra-high vacuum conditions. We observe formation of metastable domains with different work function values after annealing the material in ultra-high vacuum to moderate temperatures. We attribute these metastable values of the work function to evolution of crystal defects forming during the annealing. The experiments show that sulfur vacancies formed after exposure to elevated temperatures diffuse, coalesce, and migrate bringing the system from a metastable to equilibrium ground state. The process could be thermally activated with estimated energy barrier for sulfur vacancy migration of 0.6 eV in single unit cell MoS2. The results...


Journal of Materials Science & Technology | 2017

Safe growth of graphene from non-flammable gas mixtures via chemical vapor deposition

Ying Feng; D. Trainer; Hongshang Peng; Ye Liu; Ke Chen


Bulletin of the American Physical Society | 2018

The Effect of Applied Strain on the Quasiparticle Band-Gap of Monolayer MoS 2

D. Trainer; Yuan Zhang; F. Bobba; Xiaoxing Xi; Saw Hla; M. Iavarone


Archive | 2017

Low temperature Scanning Tunneling Microscopy investigation of FeSe single crystal

Cinzia Di Giorgio; E. Lechner; A. Putilov; D. Trainer; A. Aladyshkin; A. Melnikov; M. Abdel Hafiez; O. S. Volkova; A. N. Vasiliev; D. A. Chareev; G. Karapetrov; P. C. Canfield; R. Prozorov; M. Iavarone


Journal of Superconductivity and Novel Magnetism | 2017

Anisotropic Superconducting Gaps and Boson Mode in FeSe 1−xSx Single Crystals

C. Di Giorgio; A. Putilov; D. Trainer; O. S. Volkova; A. N. Vasiliev; D. A. Chareev; G. Karapetrov; J. F. Zasadzinski; M. Iavarone


Journal of Physics and Chemistry of Solids | 2017

Moiré superlattices and 2D electronic properties of graphite/MoS2 heterostructures

D. Trainer; A. Putilov; Baokai Wang; Christopher Lane; Timo Saari; Tay-Rong Chang; Horng-Tay Jeng; Hsin Lin; Xiaoxing Xi; Jouko Nieminen; A. Bansil; M. Iavarone


Journal of Physics D | 2017

Electrical properties of graphene tunnel junctions with high-κ metal-oxide barriers

Ying Feng; D. Trainer; Ke Chen

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G. Karapetrov

Spanish National Research Council

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D. A. Chareev

Russian Academy of Sciences

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J. F. Zasadzinski

Illinois Institute of Technology

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