carlos sanchez - Academia.edu (original) (raw)

Papers by carlos sanchez

In two-dimensional materials research, oxidation is usually considered as a common source for the... more In two-dimensional materials research, oxidation is usually considered as a common source for the degradation of electronic and optoelectronic devices or even device failure. However, in some cases a controlled oxidation can open the possibility to widely tune the band structure of 2D materials. In particular, we demonstrate the controlled oxidation of titanium trisulfide (TiS3), a layered semiconductor that attracted much attention recently thanks to its quasi-1D electronic and optoelectronic properties and its direct bandgap of 1.1 eV. Heating TiS3 in air above 300 °C gradually converts it into TiO2, a semiconductor with a wide bandgap of 3.2 eV with applications in photo-electrochemistry and catalysis. In this work, we investigate the controlled thermal oxidation of individual TiS3 nanoribbons and its influence on the optoelectronic properties of TiS3-based photodetectors. We observe a step-wise change in the cut-off wavelength from its pristine value ~1000 nm to 450 nm after sub...

Journal of Physical Chemistry C, 2009

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2002

A technique to etch GaP by reactive ion etching was developed and the effects of different etchin... more A technique to etch GaP by reactive ion etching was developed and the effects of different etching parameters were studied. Also, selective etching of GaP over AlGaP was examined and demonstrated. Etching is achieved by using SiCl 4 , which will react with GaP to form volatile compounds. Selective etching is accomplished when SiF 4 is used in addition to SiCl 4. The addition of the fluorine-based gas will result in a nonvolatile etch-inhibiting layer, AlF 3 , when aluminum is present on the sample surface. By adjusting etching parameters, a selectivity as high as 126 is demonstrated. The presence of the AlF 3 etch-inhibiting layer is verified by Auger electron spectroscopy, and the removal of this layer by buffered oxide etch is demonstrated. In addition, a direct comparison of etch rates for GaP and GaAs was made, and etch rates were found to be similar.

Applied Physics Letters, 2015

The potential of bulk black-phosphorus, a layered semiconducting material with a direct band gap ... more The potential of bulk black-phosphorus, a layered semiconducting material with a direct band gap of $0.3 eV, for thermoelectric applications has been experimentally studied. The Seebeck Coefficient (S) has been measured in the temperature range from 300 K to 385 K, finding a value of S ¼ þ335 6 10 lV/K at room temperature (indicating a naturally occurring p-type conductivity). S increases with temperature, as expected for p-type semiconductors, which can be attributed to an increase of the charge carrier density. The electrical resistance drops up to a 40% while heating in the studied temperature range. As a consequence, the power factor at 385 K is 2.7 times higher than that at room temperature. This work indicates the prospective use of black-phosphorus in thermoelectric applications such as thermal energy scavenging, which typically require devices with high performance at temperatures near room temperature. V

The electronic structure of the TiO 2 (110)-(1x2) surface has been studied by means of angular re... more The electronic structure of the TiO 2 (110)-(1x2) surface has been studied by means of angular resolved ultraviolet photoemission spectroscopy (ARUPS). The valence band dispersion along the high symmetry surface directions, [001] and [1-10], has been recorded. The experimental data show no dispersion of the band-gap Ti 3d states. However, the existence of dispersive bands along the [001] direction located at about 7eV below the Fermi Level is reported. The existence of two different contributions in the emission from the defects-related state located in the gap of the surface is univocally shown for the first time.

Chemistry - A European Journal, 2012

Since the discovery of fullerenes and the breakthrough of the synthesis of C 60 in macroscopic qu... more Since the discovery of fullerenes and the breakthrough of the synthesis of C 60 in macroscopic quantities, their fundamental properties and possible applications have been widely studied. Recently, the possibility of growing C 60 as thin films and the capability to modify them by supramolecular chemistry to add new functional molecular groups have enormously stimulated research in this field. New organic electronic devices or more efficient photovoltaic solar cells are among the technological targets. On the other hand, surface-science methods using model single-crystal surfaces in ultra-high vacuum (UHV) environments have been extensively applied to understand the fundamental properties of these organic layers. The growth of these highly controlled systems by means of a bottom-up approach permits to explore the new electronic properties and the role played by the interface between the molecular layer and the supporting substrate. Most of the studies performed until now in this direction deal with single-crystal metal surfaces, where these organic molecules frequently form well-ordered closepacked commensurate superstructures, spaced by about 11 , their van der Waals (vdW) diameter. However, although these model systems are suitable to understand the fundamental mechanisms, they are far from real applications. The next step in surface science to describe more realistic surfaces is to move towards oxide surfaces. Oxides pres-ent a much larger spectrum of real applications than metal surfaces, and most of the fundamental conclusions derived in classical surface science experiments cannot be directly extrapolated. Among these applications, fullerene-derived layers on metal oxide surfaces are some of the more active trends in the field. However, very little is known, at atomic or molecular level, about the basic mechanisms, electronic states or interface structure formed between organic molecules, such as fullerenes, and dielectric surfaces, as TiO 2 . In this work we present a full study of a prototypical organic molecule on a wide gap dielectric surface. The interface of the organic layers with the supporting dielectric is critical for determining the final electronic properties of the system. On the other hand, among all metal oxides, titanium dioxide is considered as a model for surface-science experiments since good quality surface terminations can be easily obtained. These particular features make the study of the interface between fullerene and TiO 2 appealing.

In two-dimensional materials research, oxidation is usually considered as a common source for the... more In two-dimensional materials research, oxidation is usually considered as a common source for the degradation of electronic and optoelectronic devices or even device failure. However, in some cases a controlled oxidation can open the possibility to widely tune the band structure of 2D materials. In particular, we demonstrate the controlled oxidation of titanium trisulfide (TiS3), a layered semiconductor that attracted much attention recently thanks to its quasi-1D electronic and optoelectronic properties and its direct bandgap of 1.1 eV. Heating TiS3 in air above 300 °C gradually converts it into TiO2, a semiconductor with a wide bandgap of 3.2 eV with applications in photo-electrochemistry and catalysis. In this work, we investigate the controlled thermal oxidation of individual TiS3 nanoribbons and its influence on the optoelectronic properties of TiS3-based photodetectors. We observe a step-wise change in the cut-off wavelength from its pristine value ~1000 nm to 450 nm after sub...

Journal of Physical Chemistry C, 2009

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2002

A technique to etch GaP by reactive ion etching was developed and the effects of different etchin... more A technique to etch GaP by reactive ion etching was developed and the effects of different etching parameters were studied. Also, selective etching of GaP over AlGaP was examined and demonstrated. Etching is achieved by using SiCl 4 , which will react with GaP to form volatile compounds. Selective etching is accomplished when SiF 4 is used in addition to SiCl 4. The addition of the fluorine-based gas will result in a nonvolatile etch-inhibiting layer, AlF 3 , when aluminum is present on the sample surface. By adjusting etching parameters, a selectivity as high as 126 is demonstrated. The presence of the AlF 3 etch-inhibiting layer is verified by Auger electron spectroscopy, and the removal of this layer by buffered oxide etch is demonstrated. In addition, a direct comparison of etch rates for GaP and GaAs was made, and etch rates were found to be similar.

Applied Physics Letters, 2015

The potential of bulk black-phosphorus, a layered semiconducting material with a direct band gap ... more The potential of bulk black-phosphorus, a layered semiconducting material with a direct band gap of $0.3 eV, for thermoelectric applications has been experimentally studied. The Seebeck Coefficient (S) has been measured in the temperature range from 300 K to 385 K, finding a value of S ¼ þ335 6 10 lV/K at room temperature (indicating a naturally occurring p-type conductivity). S increases with temperature, as expected for p-type semiconductors, which can be attributed to an increase of the charge carrier density. The electrical resistance drops up to a 40% while heating in the studied temperature range. As a consequence, the power factor at 385 K is 2.7 times higher than that at room temperature. This work indicates the prospective use of black-phosphorus in thermoelectric applications such as thermal energy scavenging, which typically require devices with high performance at temperatures near room temperature. V

The electronic structure of the TiO 2 (110)-(1x2) surface has been studied by means of angular re... more The electronic structure of the TiO 2 (110)-(1x2) surface has been studied by means of angular resolved ultraviolet photoemission spectroscopy (ARUPS). The valence band dispersion along the high symmetry surface directions, [001] and [1-10], has been recorded. The experimental data show no dispersion of the band-gap Ti 3d states. However, the existence of dispersive bands along the [001] direction located at about 7eV below the Fermi Level is reported. The existence of two different contributions in the emission from the defects-related state located in the gap of the surface is univocally shown for the first time.

Chemistry - A European Journal, 2012

Since the discovery of fullerenes and the breakthrough of the synthesis of C 60 in macroscopic qu... more Since the discovery of fullerenes and the breakthrough of the synthesis of C 60 in macroscopic quantities, their fundamental properties and possible applications have been widely studied. Recently, the possibility of growing C 60 as thin films and the capability to modify them by supramolecular chemistry to add new functional molecular groups have enormously stimulated research in this field. New organic electronic devices or more efficient photovoltaic solar cells are among the technological targets. On the other hand, surface-science methods using model single-crystal surfaces in ultra-high vacuum (UHV) environments have been extensively applied to understand the fundamental properties of these organic layers. The growth of these highly controlled systems by means of a bottom-up approach permits to explore the new electronic properties and the role played by the interface between the molecular layer and the supporting substrate. Most of the studies performed until now in this direction deal with single-crystal metal surfaces, where these organic molecules frequently form well-ordered closepacked commensurate superstructures, spaced by about 11 , their van der Waals (vdW) diameter. However, although these model systems are suitable to understand the fundamental mechanisms, they are far from real applications. The next step in surface science to describe more realistic surfaces is to move towards oxide surfaces. Oxides pres-ent a much larger spectrum of real applications than metal surfaces, and most of the fundamental conclusions derived in classical surface science experiments cannot be directly extrapolated. Among these applications, fullerene-derived layers on metal oxide surfaces are some of the more active trends in the field. However, very little is known, at atomic or molecular level, about the basic mechanisms, electronic states or interface structure formed between organic molecules, such as fullerenes, and dielectric surfaces, as TiO 2 . In this work we present a full study of a prototypical organic molecule on a wide gap dielectric surface. The interface of the organic layers with the supporting dielectric is critical for determining the final electronic properties of the system. On the other hand, among all metal oxides, titanium dioxide is considered as a model for surface-science experiments since good quality surface terminations can be easily obtained. These particular features make the study of the interface between fullerene and TiO 2 appealing.