First measurements of time-dependent second-harmonic generation ͑SHG͒ at a Si/(ZrO 2) x (SiO 2) 1Ϫx interface show a behavior that is drastically different from similar measurements at Si/SiO 2 interfaces. We suggest that in Si/SiO 2 only electron injection is important, while both electrons and holes contribute to the dynamics at the Si/(ZrO 2) x (SiO 2) 1Ϫx interface. Multiphoton excitation occurs in Si for all oxides, and involves direct interband transitions. The marked difference between the two systems is related to the population of multiphoton excited states in Si, the corresponding conduction-and valence-band offsets, and trapping/detrapping processes in the oxides. Our measurements confirm the existence of an initial built-in field at the interface.
We report a new and surprising enhancement of the electric field at the Si͞SiO 2 interface following the cessation of intense pulsed near-infrared radiation. The phenomenon, measured by optical secondharmonic generation, occurs only for photon energies and oxide film thickness that exceed respective thresholds. We attribute the new effect to multiphoton hole injection into the oxide and to an asymmetry in electron and hole dynamics, in particular to distinctly different trapping and detrapping processes.[S0031-9007(98)07589-9] PACS numbers: 73.50. Gr, 42.65.Ky, In this Letter, we present the first measurements of a pronounced electric field enhancement at the Si͞SiO 2 interface, which develops unexpectedly after multiphoton excitation with ultrashort laser pulses is switched off, i.e., dark conditions. We attribute this increase in the interface electric field, in the absence of external radiation, to distinctly different dynamical behavior of holes and electrons at and near the interface. Previous second harmonic generation (SHG) studies by van Driel's group [1-3] on photoexcitation at Si͞SiO 2 interfaces have elucidated the unique contribution of electrons in the development of interface electric fields.The present work establishes for the first time the important role of holes in the dynamical processes leading to charge separation and subsequent quasistatic electric field enhancement both during multiphoton excitation and also under nonperturbative conditions. Wavelength-dependent studies of this new effect show that hole injection occurs for photon energies above 1.52 eV. The subsequent field enhancement is readily observable for oxides that exceed a critical threshold thickness (approximately 30 to 40 Å). For thinner oxides hole dynamics is more complicated due to detrapping of electrons. We propose that the effect is mediated by four-photon excitation of holes across the valence-band offset, charge trapping and detrapping, and subsequent relaxation at the interface. This work bears directly on fundamental physics issues involving carrier dynamics at semiconductor interfaces, charge breakdown mechanisms, and hot carrier injection. In addition, the dependence of the new phenomenon on oxide thickness may have significant consequences on device physics as gate oxide thickness shrinks below 40 Å.For our studies, we used the optical second-harmonic generation technique, which has proved to be a sensitive probe of semiconductor interfaces [1][2][3][4][5][6][7][8][9][10][11]. The experimental setup is standard for surface SHG measurements. Briefly, a Ti:sapphire laser provides 150 fs pulses, a wavelength range tunable from 7100 to 9100 Å, and an average power of 300 mW at a repetition rate of 80 MHz. The beam is focused to approximately 10 mm in diameter on the sample, and the reflected SHG signal is measured with 0.5 s temporal resolution by a photomultiplier and photon counter. The new phenomenon was observed systematically in a variety of different oxides. A matrix of samples was prepared from lightly boron-dop...
The kelch like family member 22 (KLHL22) is a member of the KLHL (Kelch-like) gene family, which was involved in the progression of breast cancer. However, its role remains unclear in malignant melanoma (MM). Our study found that KLHL22 expression was upregulated in human MM tissues. Regarding the functional analysis for KLHL22 in the progression of MM cells, we demonstrated that overexpression of KLHL22 could promote MM cell growth in vitro. Vice versa, knockdown of KLHL22 could suppress the proliferation of MM cells. Furthermore, KLHL22 also promoted tumorigenesis of MM cells in vivo. In experiments investigating the underlying mechanism, expressions of p-Akt and p-mTOR were significantly increased by overexpression of KLHL22. Meanwhile, knockdown of KLHL22 could decrease the expression levels of p-Akt and p-mTOR. Our studies thus suggest that KLHL22 can promote the growth of MM cells via activating the PI3K/Akt/mTOR signaling pathway, which can serve as a potential target in the diagnosis and/or treatment of MM.
We report the first application of second-harmonic generation (SHG) measurements for the characterization of X-ray radiation damage in Si/SiO 2 structures. The main advantage of this experimental technique is that it is noninvasive, contactless, and sensitive to the electric field at the interface. Interaction of intense 800 nm femtosecond laser pulses with Si/SiO 2 structures results in electron-hole pair creation in the Si, multiphoton carrier injection and second-harmonic generation. The time-dependent second-harmonic (doubled frequency) signal is a measure of the dynamic electric field at the interface. This dynamic field is created and altered by unequal electron-hole injection into the oxide, trapping/detrapping of charges, and carrier recombination processes. We find that the SHG response from Si/SiO 2 samples before and after X-ray irradiation is significantly different. Thus, SHG is a promising technique for the characterization of radiation damage in Si/SiO 2 structures. In particular, SHG is especially useful in characterizing damage in ultrathin oxide layers, for which conventional electrical measurements may not be sufficiently sensitive to the kinds of defects observable via optical methods.
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