Vibrational spectroscopic imaging techniques, based on infrared absorption or Raman scattering, allow for noninvasive chemically specific visualization of biological systems. The infrared and Raman modalities with different selection rules provide complementary information. Specifically, infrared microscopy provides strong signals in the fingerprint region, but suffers from low spatial resolution. Raman microscopy provides submicrometer resolution, but requires a long acquisition time. We developed a system that combines the strengths of both techniques by integrating confocal Raman microspectroscopy to the recently developed mid-infrared photothermal microscopy. This hybrid system is capable of fast infrared photothermal imaging of living cells with submicrometer resolution to identify points of interest, followed by a full-spectrum Raman analysis of the identified objects. In addition, a fingerprint photothermal spectrum can be acquired by scanning the wavelengths of the infrared laser. Comprehensive vibrational fingerprint mapping of live cells, demonstrated in adipocytes and single bacteria, promises broad applications of this technology in biology and material science.
In this article, 2000 PPI red silicon-based AlGaInP micro-LED arrays were fabricated and investigated. The AlGaInP epilayer was transferred onto the silicon substrate via the In-Ag bonding technique and an epilayer lift-off process. The silicon substrate with a high thermal conductivity could provide satisfactory heat dissipation, leading to micro-LED arrays that had a stable emission spectrum with increasing current density from 20 to 420 A/cm2 along with a red-shift of the peak position from 624.69 to 627.12 nm (
Δ
λ
= 2.43 nm). Additionally, increasing the injection current density had little effect on the CIE (x, y) of the micro-LED arrays. Further, the I-V characteristics and light output power of micro-LED arrays with different pixel sizes demonstrated that the AlGaInP red micro-LED array on a silicon substrate had excellent electrical stability and optical output.
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