摘要 :
The frictional properties of self-assembled monolayers (SAMs) covalently bonded to silicon (Si) substrates through Si-C or Si-O-C bonds were investigated using a pin-on-plate tribometer. Four kinds of molecules with different alky...
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The frictional properties of self-assembled monolayers (SAMs) covalently bonded to silicon (Si) substrates through Si-C or Si-O-C bonds were investigated using a pin-on-plate tribometer. Four kinds of molecules with different alkyl chain lengths and different head groups were used: 1-hexadecene, 1-hexadecanol, 1-dodecene and 1-dodecanol. The SAMs with longer alkyl chains exhibited lower friction coefficients than those with shorter alkyl chains. Of the SAMs with longer alkyl chains, the SAMs with the Si-C bond of the head group exhibited lower friction coefficients, higher wear resistance and higher durability than those with the Si-O-C bond. The head group and alkyl chain length of the molecules affected the frictional properties of the modified surfaces of the SAMs.
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摘要 :
The anisotropy of the local structure around In atoms in high quality In_xGa_(1-x)N (x=0.145,0.20,0.275) single quantum wells (SQWs) was investigated by fluorescence extended x-ray absorption fine structure measurements using line...
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The anisotropy of the local structure around In atoms in high quality In_xGa_(1-x)N (x=0.145,0.20,0.275) single quantum wells (SQWs) was investigated by fluorescence extended x-ray absorption fine structure measurements using linearly polarized x ray whose electric field was set to be both horizontal and vertical to the SQWs. The interatomic distance was isotropic for the nearest In-N, whereas for the second nearest In-Ga and In-In, the interatomic distance for out-of-plane atoms was longer than that for in-plane atoms. From the analyses of the coordination number for In-In and In-Ga, the In atom distribution in the Iri_(0.275)Ga_(0.725)N SQW was found to be statistically random in both directions. On the other hand, In atoms in the In_(0.275)Ga_(0.80)N SQW, corresponding to green light-emitting diodes (LEDs), were randomly distributed in the horizontal direction but aggregated in the vertical direction. Correlation was suggested between the vertical aggregation and the higher efficiency of InGaN-based blue to green LEDs.
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Millimeter waves (30-300 GHz) are starting to be used in next generation high-speed wireless communications. To avoid electromagnetic interference in this wireless communication, finding a suitable electromagnetic wave absorber in...
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Millimeter waves (30-300 GHz) are starting to be used in next generation high-speed wireless communications. To avoid electromagnetic interference in this wireless communication, finding a suitable electromagnetic wave absorber in the millimeter wave range is an urgent matter. In this work, we prepared a high-performance millimeter wave absorber composed of a series of aluminum-substituted ￡-iron oxide, ε-Al_xFe_(2-x)O_3, nanomagnets (0 ≤ x ≤ 0.40) with a particle size between 25 and 50 nm. The materials in this series have an orthorhombic crystal structure in the Pna2_1 space group, which has four nonequivalent Fe sites and Al ion that predominantly occupies the tetrahedral [FeO_4] site. The field-cooled magnetization curves showed that the T_C values were 448, 480, and 500 K for x = 0.40, 0.21, and 0, respectively. The magnetization versus external magnetic field showed that the coercive field H_C values at 300 K were 10.2, 14.9, and 22.5 kOe for x = 0.40, 0.21, and 0, respectively. The millimeter wave absorption properties were measured at room temperature by terahertz time domain spectroscopy. The frequencies of the absorption peaks for x = 0.40, 0.30, 0.21, 0.09, 0.06, and 0 were observed at 112, 125, 145, 162, 172, and 182 GHz, respectively. These absorptions are due to the natural resonance achieved by the large magnetic anisotropies in this series. Such frequencies are the highest ones for magnetic materials. Because aluminum is the third most abundant atom, aluminum-substituted ε-iron oxide is very economical, and thus these materials are advantageous for industrial applications.
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摘要 :
The friction and wear properties of phosphor bronze discs sliding against SAE52100 steel balls were evaluated using an Optimol SRV reciprocating friction and wear tester under the lubrication of pure poly-alpha-olefin (PAO) and PA...
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The friction and wear properties of phosphor bronze discs sliding against SAE52100 steel balls were evaluated using an Optimol SRV reciprocating friction and wear tester under the lubrication of pure poly-alpha-olefin (PAO) and PAO containing commercial phosphite ester, zinc dialkyldithiophosphate (ZDTP) and oleic acid additives. The morphologies of the worn surfaces of the phosphor bronze discs were observed using a scanning electron microscope (SEM). In addition, the elemental compositions and chemical states of several typical elements on the worn surfaces of the phosphor bronze discs were examined by means of X-ray photoelectron spectroscopy (XPS). The findings indicated that the phosphor bronze discs exhibited higher wear resistance under the lubrication of PAO containing phosphite ester than pure PAO, PAO containing ZDTP, and PAO containing oleic acid. Also, the phosphor bronze discs exhibited stable friction coefficients as low as 0.09-0.11 when lubricated with PAO containing phosphite ester. According to the XPS analyses, it was considered that the formation of CuO and phosphate led to lower friction coefficient and high wear resistance of phosphor bronze specimens lubricated with PAO containing phosphite ester. In the case of the phosphor bronze specimens lubricated with PAO containing ZDTP and oleic acid, the formation of organic compounds seemed to lead to lower friction coefficient, but did not seem to affect the wear resistance.
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