Adriana Rivera | Universidad de Puerto Rico, Rio Piedras (original) (raw)

Papers by Adriana Rivera

Journal of Applied Physics, 2016

Thermal stability of quasi particles, i.e., exciton and trion, and a strong particle-particle int... more Thermal stability of quasi particles, i.e., exciton and trion, and a strong particle-particle interaction significantly tune the optical properties of atomically thin two dimensional (2D) metal dichalcogenides. The present work addresses the effect of inherent defects upon optical properties of chemical vapor deposition grown 1 L-WS 2 and proposes the use of chemical transfer doping as a reversible and simple method for identification of the type of excess charge in the system. Photoluminescence (PL) studies in pristine 1 L-WS 2 show that an additional band at $0.06 eV below trion (X 6) PL band was evolved (at low temperature) which was associated to the bound exciton with charged/ neutral defect. Using 7,7,8,8-Tetracyanoquinodimethane and 2,2-bis1,3-dithiolylidene as p and n-type dopants, respectively, we determined that the inherent defects/metal vacancies, which could be due to the presence of Tungsten metal deficiency, contributed in p-type nature of the pristine 1 L-WS 2. Doping of 2D transition metal dichalcogenides materials with organic molecule via the surface charge transfer method is not only a way to provide a handy way to tailor the electronic and optical properties but also can be used as a tool to determine the nature of defects in the material.

Applied Physics Letters, 2016

Nanostructured materials such as carbon nanotubes are excellent cold cathode emitters. Here we re... more Nanostructured materials such as carbon nanotubes are excellent cold cathode emitters. Here we report comparative field emission (FE) studies on topographically-tailored few layer MoS 2 films consist of <0001> plane perpendicular (⊥) to c-axis (i.e. edge terminated vertically aligned) along with planar few layer and monolayer (1L) MoS 2 films. FE measurements exhibited lower turn-on field E to (defined as required applied electric field to emit current density of 10 µA/cm 2), ~4.5 V/µm and higher current density ~1 mA/cm 2 , for edge terminated vertically aligned (ETVA) MoS 2 films. However, E to magnitude for planar few layer and 1L MoS 2 films increased further to 5.7 and 11 V/µm respectively, with one order decrease in emission current density. The observed differences in emission behavior, particularly for ETVA MoS 2 is attributed to the high value of geometrical field enhancement factor (β), found to be ~1064, resulting from the large confinement of localized electric field at edge exposed nanograins. Emission behavior of planar few layers and 1L MoS 2 films are explained under a two step emission mechanism. Our studies suggest that the with further tailoring the microstructure of ultra thin ETVA MoS 2 films would result in elegant FE properties.

Applied Physics Letters, 2019

Charge doping in transition metal dichalcogenide is currently a subject of high importance for fu... more Charge doping in transition metal dichalcogenide is currently a subject of high importance for future electronic and optoelectronic applications. Here we demonstrate chemical doping in CVD grown monolayer (1L) of WS2 by a few commonly used laboratory solvents by investigating the room temperature photoluminescence (PL). The appearance of distinct trionic emission in the PL spectra and quenched PL intensities suggest n-type doping in WS2. The temperature-dependent PL spectra of the doped 1L-WS2 reveal significant enhancement of trion emission intensity over the excitonic emission at low temperature indicating the stability of trion at low temperature. The temperature dependent exciton-trion population dynamic has been modeled using the law of mass action of trion formation. These results shed light on the solution-based chemical doping in 1L WS2 and its profound effect on the photoluminescence which is essential for the control of optical and electrical properties for optoelectronics applications.

Journal of Applied Physics, 2016

Thermal stability of quasi particles, i.e., exciton and trion, and a strong particle-particle int... more Thermal stability of quasi particles, i.e., exciton and trion, and a strong particle-particle interaction significantly tune the optical properties of atomically thin two dimensional (2D) metal dichalcogenides. The present work addresses the effect of inherent defects upon optical properties of chemical vapor deposition grown 1 L-WS 2 and proposes the use of chemical transfer doping as a reversible and simple method for identification of the type of excess charge in the system. Photoluminescence (PL) studies in pristine 1 L-WS 2 show that an additional band at $0.06 eV below trion (X 6) PL band was evolved (at low temperature) which was associated to the bound exciton with charged/ neutral defect. Using 7,7,8,8-Tetracyanoquinodimethane and 2,2-bis1,3-dithiolylidene as p and n-type dopants, respectively, we determined that the inherent defects/metal vacancies, which could be due to the presence of Tungsten metal deficiency, contributed in p-type nature of the pristine 1 L-WS 2. Doping of 2D transition metal dichalcogenides materials with organic molecule via the surface charge transfer method is not only a way to provide a handy way to tailor the electronic and optical properties but also can be used as a tool to determine the nature of defects in the material.

Applied Physics Letters, 2016

Nanostructured materials such as carbon nanotubes are excellent cold cathode emitters. Here we re... more Nanostructured materials such as carbon nanotubes are excellent cold cathode emitters. Here we report comparative field emission (FE) studies on topographically-tailored few layer MoS 2 films consist of <0001> plane perpendicular (⊥) to c-axis (i.e. edge terminated vertically aligned) along with planar few layer and monolayer (1L) MoS 2 films. FE measurements exhibited lower turn-on field E to (defined as required applied electric field to emit current density of 10 µA/cm 2), ~4.5 V/µm and higher current density ~1 mA/cm 2 , for edge terminated vertically aligned (ETVA) MoS 2 films. However, E to magnitude for planar few layer and 1L MoS 2 films increased further to 5.7 and 11 V/µm respectively, with one order decrease in emission current density. The observed differences in emission behavior, particularly for ETVA MoS 2 is attributed to the high value of geometrical field enhancement factor (β), found to be ~1064, resulting from the large confinement of localized electric field at edge exposed nanograins. Emission behavior of planar few layers and 1L MoS 2 films are explained under a two step emission mechanism. Our studies suggest that the with further tailoring the microstructure of ultra thin ETVA MoS 2 films would result in elegant FE properties.

Applied Physics Letters, 2019

Charge doping in transition metal dichalcogenide is currently a subject of high importance for fu... more Charge doping in transition metal dichalcogenide is currently a subject of high importance for future electronic and optoelectronic applications. Here we demonstrate chemical doping in CVD grown monolayer (1L) of WS2 by a few commonly used laboratory solvents by investigating the room temperature photoluminescence (PL). The appearance of distinct trionic emission in the PL spectra and quenched PL intensities suggest n-type doping in WS2. The temperature-dependent PL spectra of the doped 1L-WS2 reveal significant enhancement of trion emission intensity over the excitonic emission at low temperature indicating the stability of trion at low temperature. The temperature dependent exciton-trion population dynamic has been modeled using the law of mass action of trion formation. These results shed light on the solution-based chemical doping in 1L WS2 and its profound effect on the photoluminescence which is essential for the control of optical and electrical properties for optoelectronics applications.