Gas Sensitivity Properties Of Nano-sized Carbon/Silicon Heterojunctions Fabricated By Magnetron Sputtering

Ammonia (NH3) sensors based on carbon/sillicon (C/Si) heterojunctions are demonstrated at room temperature (RT). Upon exposure to ammonia (0.2 ml/l) at RT, the interface capacitance of C/Si junction increases dramatically about 230%. The results show that C/Si junctions have high NH3 gas sensitivity, rapid response and high recovery speed at RT. This phenomenon can be attributed to the change of potential barrier width of the junction, which is caused by the adsorption of NH3 molecules. The C/Si junctions can greatly amplify the detection sensitivity of the nano-sized carbon so that the C/Si junctions allow acting as excellent RT gas sensors.Carbon nanotip arrays were grown from silicon substrates via direct current magnetron sputtering at RT. The simple carbon nanotip arrays/n-Si (CNA/Si) heterojunctions were used to detect ethanol gas at RT. The results show that the CNA/Si junctions have high ethanol gas sensitivity, rapid response and high recovery speed at RT. Upon exposure to ethanol gas (0.64 g/L) at RT, the resistance of the junction decreases by 35% at a given positive voltage of 8 V. And the interface capacitance of the junction at 5 kHz can increase by about 40% rapidly when exposed to ethanol gas. The phenomena should be attributed to the change of the Fermi level of the carbon film caused by adsorbing electrons from ethanol molecules. The study shows that the CNA/Si junctions have potential application as ethanol gas sensors.Amorphous carbon (a-C) films were deposited on n-silicon by direct current magnetron sputtering at RT and the corresponding microstructure was characterized. The RT capacitive humidity sensing properties of C/Si junctions were studied by a standard two-probe method. It was shown that with the RH changing from 11 to 95%, a capacitive device response over 200% was achieved at 1 kHz, and the curve of the capacitive response with RH is of high linearity at the given frequency range. The phenomena should be attributed to the change of the Fermi level of carbon film caused by adsorbing electrons from H2O molecules. The result also shows that the capacitance of the junctions increases with decreasing frequency, because the adsorbed water molecules can get stronger polarization at lower frequencies. The study shows that the C/Si junctions have potential application as humidity gas sensors.Using magnetron sputtering method we prepared Pd x C1-x composite films and a-C films on n-Si (100) substrates. Then the electrical properties and the hydrogen sensitive properties of the Pdx C1-x/Si junctions were explored. The results showed that: (1) the palladium-doped carbon films contain higher sp2 carbon structure, induced by palladium atoms, than the pure carbon films; (2) the resistivity of Pdx C1-x films is larger than that of pure carbon films by 3 orders of magnitude; (3) the Pd x C1-x/Si junctions can be used to detect hydrogen gas, because the conductivity of the Pdx C1-x film is sensitive to hydrogen.