Contrasting photovoltaic response and photoluminescence for distinct porous silicon pore structures

Gole, James L.; Devincentis, Julie A.; Seals, Lenward; Lillehei, Peter T.; Narasimha, S.

doi:10.1103/physrevb.61.7589

Cited by 8 publications

(8 citation statements)

References 47 publications

(57 reference statements)

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“…Whereas PS fabricated from aqueous electrolytes consists of highly nanoporous branched structures, PS fabricated from nonaqueous electrolytes is comprised of open and accessible microporous structures (p-micropores 19 ) with deep, wide, well-ordered channels . Taking advantage of this distinction, Gole et al developed a procedure to form microporous structures with nanoporous sidewalls. These hybrid microporous/nanoporous structures display a dramatically different photovoltaic (PV) response versus either crystalline silicon or nanoporous PS generated using an aqueous etch procedure.…”

Section: Introductionmentioning

confidence: 99%

Optical Analysis of the Light Emission from Porous Silicon: A Hybrid Polyatom Surface-Coupled Fluorophor

Gole¹,

Veje²,

Egeberg

et al. 2006

J. Phys. Chem. B

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The most extensive data set yet generated correlating photoluminescence excitation (PLE) and photoluminescence (PL) spectra is presented for aged (equilibrated) porous silicon (PS) samples. The observed features, which are temperature independent over the range 10-300 K, show a detailed correlation with the results of photoacoustic spectroscopy (PAS) and with molecular electronic structure calculations. The observed energy level patterns are reproduced in the photoabsorption (PA) of PS films released after the etching of a silicon wafer. It is concluded that the energy level pattern found for the photoluminescing surface of PS results from a structure which is neither uniquely molecule- or bulk-like but represents a hybrid form for which the density of states associated with a polyatomic vibrationally excited surface-bound fluorophor dominates the nature of the observed features which are not those of a semiconductor. These fluorophor features are broadened and shifted to lower excitation energy as a result of the intimate presence of the silicon surface to which the fluorophor is bound. The dominance of the surface-bound fluorophor accounts for the temperature-independent PLE and PL features. The observed spectral features are thus suggested to be the result of a strong synergistic interaction in which the silicon surface influences the location of surface-bound fluorophor excited states whereas the nature of the vibrationally excited surface-bound fluorophor coupling to the silicon surface provides the mechanism for an enhanced vibronic structure dominated interaction and energy transfer. The observed PLE, PL, PAS, and PA measurements are found to be consistent with previous photovoltaic and photoconductivity measurements, correlating well with a surface-bound oxyhydride-like emitter. This study suggests the important role that the overtone structure of a molecule bound to a surface can play as one forms a hybrid system.

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Section: Introductionmentioning

confidence: 99%

Optical Analysis of the Light Emission from Porous Silicon: A Hybrid Polyatom Surface-Coupled Fluorophor

Gole¹,

Veje²,

Egeberg

et al. 2006

J. Phys. Chem. B

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“…The development of devices based on the porous silicon PL, while a focus of considerable effort, has been slowed by (1) the inability to enhance and stabilize this PL for long periods and (2) the inability to obtain a low resistance contact to the PS surface as typical resistances are of the order kΩ→MΩ. In overcoming this primary limitation in the application of PS, we have demonstrated that the PL from nanoporous or hybrid macroporous-nanoporous PS structures can be greatly enhanced and stabilized through treatment with aqueous HC1/methanol solutions [17,19]. More recently, based on this PL enhancement, we have developed a technique for the selective patterned metallization of a porous silicon (PS) surface using the photoluminescent surface as a reducing agent [20].…”

Section: Porous Silicon Sensorsmentioning

confidence: 99%

“…The electrochemical etching of silicon in a variety of electrolytes can produce a bewildering multitude of sizes and shapes [6,7]. Pore sizes can be made to vary [8][9][10][11][12][13][14][15] from the 1-10 nm range [8] to sizes of the order of 3 µm [15] and mixtures of two pore types are possible [9,[16][17][18]. Porous silicon (PS) formed from the HF-based etch of a silicon wafer is characterized by an extensive visible photoluminescence (PL) which when excited by uv radiation displays a time dependent behavior resulting primarily from surface-based oxidation processes.…”

mentioning

confidence: 99%

“…Porous silicon (PS) formed from the HF-based etch of a silicon wafer is characterized by an extensive visible photoluminescence (PL) which when excited by uv radiation displays a time dependent behavior resulting primarily from surface-based oxidation processes. The first time dependent PL histograms recorded for PS reflect the summation of light emission over a number of sites on the PS surface [17,18] as they demonstrate the evolution of surface bound emitters extending and transforming from the blue-green to the orangered region of the spectrum within a time scale extending from 1.5 up to 70 µseconds following the uv excitation. The development, enhancement, and evolution of this PL can be significantly influenced through the introduction of a variety of surface treatments with, for example, HCl [17] and select dyes [16].…”

mentioning

confidence: 99%

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From nanostructures to porous silicon: sensors and photocatalytic reactors

Gole

Fedorov

Hesketh

et al. 2004

phys. stat. sol. (c)

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A rapid, reversible, and sensitive porous silicon (PS) gas sensor, based upon a uniquely formed highly efficient electrical contact to a nanopore covered microporous array, is modified to introduce selectivity and for the purpose of a novel heterogeneous photocatalytic reactor. Utilizing photoluminescence induced electroless metallization as a means of obtaining a highly efficient electrical contact we demonstrate the detection of HC1, NH 3 , CO and NO at the ppm level. The response of this device, which operates with limited sensitivity at a bias voltage of 1-10 mV, is rapid and reversible. The form of metallization used to establish a low resistance, 20 Ω, contact also provides the basis for more efficient electroluminescent devices. After an electroless gold treatment, the impedance response of the device to ammonia increases by 2.5 times, while the CO and NO responses are unchanged. With an electroless tin coating, the room temperature responses to NH 3 , NO, and CO are all amplified. With an FFT analysis, a gas response can now be acquired and filtered on a drifting baseline, further increasing sensitivity. These sensor suites are now being extended to develop microreactors in which nanoscale quantum dot (QD) photocatalysts will be placed within the pores of PS and excited using PS electroluminescence or photoluminescence to excite visible light absorbing QDs. Visible light absorbing titania-based QDs have been developed. Using a nanoscale exclusive synthesis route, we directly treat TiO 2 nanocolloids and, in seconds, at room temperature, we produce nitrogen doped, stable, and environmentally benign TiO 2-x N x photocatalysts whose optical response, now not limited to the ultraviolet, can be tuned across the entire visible region. This synthesis, which can be simultaneously accompanied by metal atom seeding, can be accomplished through the direct nitration of anatase TiO 2 nanostructures with alkyl ammonium salts. Tunability throughout the visible depends on the degree of TiO 2 nanoparticle agglomeration and the influence of metal seeding. No organics are incorporated into the final TiO 2-x N x products. These visible light absorbing photocatalysts readily photodegrade methylene blue and gaseous ethylene. They can be transformed from liquids to gels and placed on the surfaces of sensor and microreactor based configurations 1) to produce an improved photocatalytically induced solar based sensor response, and 2) with a goal to facilitate catalytically induced disinfection of airborne pathogens. In contrast to a nitridation process which is facile at the nanoscale, we find little or no direct nitridation of micrometer sized anatase or rutile TiO 2 powders at room temperature. Thus, we demonstrate an example of how a traversal to the nanoscale can vastly improve the efficiency for producing important submicron particles.

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“…The hybrid samples were etched with a current density of 6 mA/cm2 for between 50 and 75 min. Using this procedure, pores approximately 1 µ m wide and 10 µ m deep were formed, well covered by a coating of nanoporous silicon 42,43 .…”

Section: Photoluminescence Characterizationmentioning

confidence: 99%

Nanostructure and morphology modified porous silicon sensors

Gole

Lewis

2005

SPIE Proceedings

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The ability to control and transform the morphology and optical properties of porous silicon (PS) interface arrays can have important implications for displays and sensors. .The optoelectronic properties and interaction sensing capabilities of PS can be varied as a function of pore size and pore morphology as dictated by the manipulation of a surface structure which can be controlled with current density, the solution composition of the electrochemical etches used to prepare the pores, and careful post etch surface treatments. These treatments influence the time dependent photoluminescence (PL) emission from PS. The variation of surface structure as it effects the PL from these PS pore arrays is outlined and discussed within the framework of detailed molecular electronic structure calculations which model the excited state structure giving rise to the UV-visible PL emission from PS. Applications varying from displays to sensors to micro-reactors will be considered. Porous silicon interfaces have also been transformed within the framework of nanotechnology to create highly efficient sensors displaying a rapid, reversible, sensitive, and selective response to HCl, NH 3 , CO, and NO down to the ppb level. Photoluminescence induced metallization is used to obtain a highly efficient, <20Ω, electrical contact to the sensor, allowing operation at a bias voltage of 1-10mV. The introduction of gold and tin-based nanostructures to a micro/nanoporous PS array selectively modifies its impedance response to considerably improve the detection of the NH 3 , CO, and NO. Through FFT analysis, a gas response can be acquired and filtered on a drifting baseline, further improving sensitivity. New nanoscale exclusive techniques have been developed for the rapid formation of highly efficient TiO 2-x N x nanophotocatalysts, operative and tunable throughout the visible wavelength region, to be used in conjunction with porous silicon hybrid nanopore coated micropores to form novel and efficient solar pumped sensor arrays.

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Contrasting photovoltaic response and photoluminescence for distinct porous silicon pore structures

Cited by 8 publications

References 47 publications

Optical Analysis of the Light Emission from Porous Silicon: A Hybrid Polyatom Surface-Coupled Fluorophor

Optical Analysis of the Light Emission from Porous Silicon: A Hybrid Polyatom Surface-Coupled Fluorophor

From nanostructures to porous silicon: sensors and photocatalytic reactors

Nanostructure and morphology modified porous silicon sensors

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