Dataset for the comparison of vacuum-treated and as-etched porous silicon samples in terms of the evolution of oxidation at low temperatures.

The development of chemical sensors made from porous silicon is a task that has been addressed for several years. In order to have a reliable sensing material, stability must be guaranteed. Oxidation in silicon degrades the sensing capability. The data presented in this article provides some important insights concerning the treatment of samples that can improve the material stability against oxidation. For this purpose, Fourier Transformed Infrared (FTIR) measurements using an Attenuated Total Reflectance (ATR) additament were employed to extract information concerning oxidation on the samples submitted to different temperatures. Photoluminescent (PL) measurements were also performed on the samples in order to extract information on nanocrystals sizes and their relationship with oxidation.


Specifications table
Materials Chemistry Specific subject area Semiconductor surfaces electrochemical treatment to produce nanocrystalline material for the development of new chemical sensors Type of data Table  Graph How data were acquired • ATR data: FTIR spectroscopy using instrument with ATR additament.
• Photoluminescence (PL) data: UV/VIS spectroscopy using a CCD-based spectrometer, a UV laser as a light source and fiber optics. • Data fittings: PeakFit software and already published models for fitting methodology. Data format Raw Analyzed Parameters for data collection All data were acquired in a closed laboratory room, with relative humidity around 40% and a temperature near 20 °C. ATR measurements required an additament with varying temperature capability. PL data were recorded using a 5 mW laser and optical density filters for attenuation. All data processes (plotting, fitting) were performed using desktop computers. Description of data collection ATR: Setting of working temperature by an external controller and wait a few minutes for stabilization; reflectance data acquisition from software-driven instrument; software data process to exchange reflectance to absorbance measurements.

Value of the Data
• Data provides valuable information concerning the comparison between porous silicon samples stored in high vacuum right after synthesis and non-treated samples (as-etched). • Materials scientists and engineers developing chemical sensors can benefit from these data.
• These data are useful in the study of oxidation effects in the semiconductor, providing a better understanding of the material.

Data description
The main data files can be retrieved in the link provided in appendix A. FTIR-ATR Absorbance data for as-etched samples and vacuum treated samples (see details in the next section) for different temperatures from 21 °C to 202 °C are provided. Fig. 1 shows a plot for an as-etched sample at 21 °C. Some important features are also shown. The importance of the SiOSi and SiH band are fully discussed in [1] . Tables 1 and 2 show the temperatures, inverse temperature, amplitude of SiH peak, amplitude of SiOSi peak and SiOSi-to-SiH amplitude ratios for the As-etched sample ( Table 1 ) and Vacuum treated sample ( Table 2 ). The amplitudes can be extracted from the FTIR-ATR data mentioned above. Fig. 2 plots the SiOSi/SiH ratio against the inverse temperature for both kinds of samples. The behaviors are different and are explained in [1] .

Table 1
Temperatures, inverse temperature, peak amplitude of modes and ratio of amplitudes for the As-etched sample.
Temp ( °C) Temp (K) 10 0 0/T (K −1 ) Amplitude SiH peak at 620 cm −1 Amplitude SiOSi peak at 1063 cm −   Data files also contain PL measurements of As-etched and Vacuum treated samples for three temperatures: 21 °C, 83 °C and 130 °C. As an example, Fig. 3 shows PL plots in the visible region of the As-etched and the Vacuum treated samples after being exposed to a temperature of 83 °C. From these data, contributions from quantum dots (QD), quantum wires (QW) and their surface localized states (Loc. States) can be extracted according to the methodology explained in [2] .

Experimental design, materials, and methods
PSi samples were obtained from Boron-doped crystalline Silicon, (100) surface indices, and 20-50 Ohm-cm resistivity using an electrochemical etching cell filled with an ethanoic HF solution at 12.5% of acid concentration. A constant current density of 54 mA.cm −2 was used in the process for a 6 min etching time. The samples were subsequently classified into two groups: the ones with no further treatment after production, were named as-etched , whereas those who were exposed to a high vacuum system using turbomolecular pumps (base pressure below 1 × 10 −6 Torr for at least 24 h) were named vacuum treated . For both kinds of samples, the following surface characterizations were performed: Fourier Transformed Infrared spectroscopy with Attenuated Total Reflectance additament (FTIR-ATR, Frontier model of PerkinElmer employing a diamond crystal in contact with the samples, in the energy range from 550 to 40 0 0 cm −1 . Infrared measurements with temperature variation could be obtained using a Pike GladiATR accessory connected to the Frontier FTIR. The temperature ranged from 21 °C to 201 °C. In these circumstances, the whole oxidation process took less than one hour. Photoluminescence (PL) data were recorded using a two-channel Ocean Optics (model SD-20 0 0) spectrophotometer with a 447 nm laser as a light source connected with a fiber-optic probe. PL analysis to extract nanocrystalline parameters was performed as indicated in [2] .