研究目的
Analyzing the influence of barium fluoride thin and ultra-thin film thickness and chemical composition on the work function of the resulting heterostructure for thermionic-thermophotovoltaic applications.
研究成果
A work function of 2.1 eV is achieved for an ultra-thin layer of barium fluoride on p-type GaAs surface, with a significant reduction from bare GaAs. The optimal Ba/F stoichiometric ratio is around 1.0, and the minimal work function is obtained with a nominal thickness of 2 nm. Thermionic measurements confirm the work function reduction, making barium fluoride thin films appealing for thermionic and TIPV devices operating at ultra-high temperatures.
研究不足
The nominal thickness must be considered only a reference value due to the rough estimation from the quartz microbalance. The work function estimation from thermionic measurements may be affected by possible desorption caused by anode heating.
1：Experimental Design and Method Selection:
Electron-beam evaporation was used for the deposition of BaF2 films on GaAs substrates. X-ray photoemission spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) were employed to analyze the film's chemical composition and work function. Thermionic emission measurements were performed to confirm the work function reduction.
2：Sample Selection and Data Sources:
Doped (p-type) GaAs (100) single-crystal wafers were used as substrates. BaF2 pellets (purity 99.9%) were the source material for evaporation.
3：9%) were the source material for evaporation.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Electron beam evaporation system, quartz microbalance for thickness monitoring, FEG-SEM for surface morphology analysis, ESCALAB 250Xi for XPS and UPS measurements, thermionic converter test device.
4：Experimental Procedures and Operational Workflow:
GaAs substrates were cleaned before deposition. BaF2 films of varying thicknesses were deposited. XPS and UPS measurements were conducted to analyze the films. Thermionic emission measurements were performed to evaluate the work function.
5：Data Analysis Methods:
XPS and UPS data were processed using Avantage v.5 software. Work function was calculated from UPS spectra. Thermionic emission data were analyzed to estimate work function reduction.
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