Search

Scaffolded molecular networks are important building blocks in biological pigment–protein complexes, and DNA nanotechnology allows analogous systems to be designed and synthesized. System–environment interactions in these systems are responsible for important processes, such as the dissipation of heat and quantum information. This study investigates the role of nanoscale molecular parameters in tuning these vibronic system–environment dynamics. Here, genetic algorithm methods are used to obtain nanoscale parameters for a DNA-scaffolded chromophore network based on comparisons between its calculated and measured optical spectra. These parameters include the positions, orientations, and energy level characteristics within the network. This information is then used to compute the dynamics, including the vibronic population dynamics and system–environment heat currents, using the hierarchical equations of motion. The dissipation of quantum information is identified by the system's transient change in entropy, which is proportional to the heat currents according to the second law of thermodynamics. These results indicate that the dissipation of quantum information is highly dependent on the particular nanoscale characteristics of the molecular network, which is a necessary first step before gleaning the systematic optimization rules. Subsequently, the I-concurrence dynamics are calculated to understand the evolution of the vibronic system's quantum entanglement, which are found to be long-lived compared to these system–bath dissipation processes. [ABSTRACT FROM AUTHOR]

DNA nanotechnology has now enabled the self-assembly of almost any prescribed 3-dimensional nanoscale structure in large numbers and with high fidelity. These structures are also amenable to site-specific modification with a variety of small molecules ranging from drugs to reporter dyes. Beyond obvious application in biotechnology, such DNA structures are being pursued as programmable nanoscale optical breadboards where multiple different/identical fluorophores can be positioned with sub-nanometer resolution in a manner designed to allow them to engage in multistep excitonic energy-transfer (ET) via Förster resonance energy transfer (FRET) or other related processes. Not only is the ability to create such complex optical structures unique, more importantly, the ability to rapidly redesign and prototype almost all structural and optical analogues in a massively parallel format allows for deep insight into the underlying photophysical processes. Dynamic DNA structures further provide the unparalleled capability to reconfigure a DNA scaffold on the fly in situ and thus switch between ET pathways within a given assembly, actively change its properties, and even repeatedly toggle between two states such as on/off. Here, we review progress in developing these composite materials for potential applications that include artificial light harvesting, smart sensors, nanoactuators, optical barcoding, bioprobes, cryptography, computing, charge conversion, and theranostics to even new forms of optical data storage. Along with an introduction into the DNA scaffolding itself, the diverse fluorophores utilized in these structures, their incorporation chemistry, and the photophysical processes they are designed to exploit, we highlight the evolution of DNA architectures implemented in the pursuit of increased transfer efficiency and the key lessons about ET learned from each iteration. We also focus on recent and growing efforts to exploit DNA as a scaffold for assembling molecular dye aggregates that host delocalized excitons as a test bed for creating excitonic circuits and accessing other quantum-like optical phenomena. We conclude with an outlook on what is still required to transition these materials from a research pursuit to application specific prototypes and beyond. [ABSTRACT FROM AUTHOR]

A voltage-controlled-oscillator (VCO) circuit has been designed for radiation-hardened-by-design (RHBD) single-event transient (SET) mitigation. The RHBD technique, which can be readily implemented in mixed-signal phase-locked loops and delay-locked loops, is shown to substantially improve the single-event performance of the VCO while decreasing the rms phase jitter due to power supply noise. Additionally, using the probabilistic analysis technique presented, the RHBD VCO shows a maximally improved SET response over that of the conventional VCO, decreasing the output phase displacement to below the nominal phase jitter. Index Terms--Delay-locked loops, phase-locked loops, radiation effects, radiation hardening, single-event transients, voltage-controlled oscillators.

Single-photon (SPA) and two-photon laser absorption (TPA) techniques are established as reliable, effective methods to study specific single-event (SE) phenomena in advanced CMOS technologies. However, dense metal-fill in these nanoscale processes can prevent the use of top-side SPA in some cases. This paper demonstrates a novel methodology enabling top-side laser SPA single-event effects (SEEs) measurements in the presence of dense metal-fill for a test circuit fabricated in a commercial 90 nm CMOS process and validates it using unimpeded, through-wafer TPA approach. This is achieved by measuring and comparing the SEU thresholds for the sample circuit using both techniques. Index Terms--Complementary metal-oxide-semiconductor (CMOS), laser, metal-fill, single event (SE), single-photon absorption (SPA), two-photon absorption (TPA).

An on-chip charge-collection measurement circuit has been designed and fabricated in a 130 nm bulk CMOS process. Laser testing is used to verify the effectiveness of the on-chip charge-collection circuit technique for characterizing single event charge collection in advanced technologies. The on-chip charge-collection measurement circuit is used as an investigative tool for examining the effects of parasitic bipolar amplification for deep.submicron PMOS devices. Index Terms--Charge collection, [n.sup.+] diode, NMOS, n-well potential collapse, [p.sup.+] diode, parasitic bipolar transistor, PMOS, single event characterization.

Device-level current transients are induced by injecting carriers using two-photon absorption from a subbandgap pulsed laser and recorded using wideband transmission and measurement equipment. These transients exhibit three distinct temporal trends that depend on laser pulse energy as well as the transverse and vertical charge generation location. The nature of the current transient is controlled by both the behavior of the subcollector-substrate junction and isolation biasing. However, substrate potential modulation, due to deformation of the subcollector-substrate depletion region, is the dominant mechanism affecting transient characteristics. Index Terms--Current transient, electrostatic potential modulation, SiGe HBT, two-photon absorption.

Recent measurements of heavy-ion-induced charge-collection transients are presented. These measurements are possible for the first time because of recent developments in highbandwidth, single-shot measurement technology, and exhibit several significant advantages over conventional (charge-sensitive preamplifier) charge-collection measurements. Heavy-ion induced transient measurements are presented for InGaAs/InAIAs HEMTs, AISb/InAs HEMTs, GaAs HFETs and for SOI NMOS devices, and the significant advantages of this approach are described. Index Terms--AISb/InAs HEMT, charge collection, InGaAs HEMT, laser SEE, single event effects, SOI, transient measurement.

Fast and efficient Forster energy transfer from a blue-emitting host (4,4-bis[N-1-naphthyl-N-phenylamino]biphenyl, alpha-NPD) to a red-emitting dioxolane-substituted pentacence derivative (2,2,10-tetraethyl-6-14-bis(triisopropylsilylethynyl)-1,3,9,11-tetraoxadicyclopenta[b,m]pentacene, EtTP-5) is demonstrated. The concentrated films have shown less evidence of aggregation when EtTP-5 was dispersed in tris(quinolin-8-olato)aluminum(III), making alpha-NPD a superior host for the red emitting EtTP-5.

Sequence-selective bis-intercalating dyes exhibit large increases in fluorescence in the presence of specific DNA sequences. This property makes this class of fluorophore of particular importance to biosensing and super-resolution imaging. Here we report ultrafast transient anisotropy measurements of resonance energy transfer (RET) between thiazole orange (TO) molecules in a complex formed between the homodimer TOTO and double-stranded (ds) DNA. Biexponential homo-RET dynamics suggest two subpopulations within the ensemble: 80% intercalated and 20% non-intercalated. Based on the application of the transition density cube method to describe the electronic coupling and Monte Carlo simulations of the TOTO/dsDNA geometry, the dihedral angle between intercalated TO molecules is estimated to be 81° ± 5°, corresponding to a coupling strength of 45 ± 22 cm-1. Dye intercalation with this geometry is found to occur independently of the underlying DNA sequence, despite the known preference of TOTO for the nucleobase sequence CTAG. The non-intercalated subpopulation is inferred to have a mean inter-dye separation distance of 19 Å, corresponding to coupling strengths between 0 and 25 cm-1. This information is important to enable the rational design of energy transfer systems that utilize TOTO as a relay dye. The approach used here is generally applicable to determining the electronic coupling strength and intercalation configuration of other dimeric bis-intercalators. [ABSTRACT FROM AUTHOR]

The single-event upset response of a single-event hardened SRAM 10-transistor cell is mapped in two dimensions via carrier injection by two-photon absorption through the back (substrate) surface in a flip-chip mounted 4 Mb SRAM. Using through-wafer carrier injection, charge is deposited into the active regions of the device at well-defined locations in a reproducible manner, and the single-event upset sensitive region of the device is localized to within [+ or -]0.3 micrometers. Index Terms--Laser SEE, nonlinear absorption, single-event effects, SEE, SEU, silicon, SRAM.

Heavy ion irradiation was simulated using a Geant4 based Monte-Carlo transport code. Electronic and nuclear physics were used to generate statistical profiles of charge deposition in the sensitive volume of an SEU hardened SRAM. Simulation results show that materials external to the sensitive volume can affect the experimentally measured cross-section curve. Index Terms--Cross section, Geant4, MRED, single event upset.

The first demonstration of through-wafer two-photon absorption (TPA) single-event effects (SEEs) testing is presented. We interrogate the single-event transient (SET) response of several different nodes of the LM124 operational amplifier via TPA carrier injection through both the front and back (substrate) chip surfaces. The results reveal that the SETs and sensitivities produced in several different nodes by front-side and back-side irradiation are effectively identical, confirming the validity of this approach for SEE studies. Index Terms--LM124 operational amplifier, multiphoton absorption, nonlinear absorption, nonlinear-optical carrier injection, single-event effects (SEE), single-event transients (SET).

The single-event effects response of three different III-V field-effect transistor technologies (GaAs MESFET, InAIAs/InGaAs HEMT, and AISb/InAs HEMT) is measured for MeV and GeV heavy-ion irradiation. These measurements reveal significant charge enhancement and very slow, microsecond-timescale relaxation times for the GaAs and InAIAs/InGaAs devices, with a much faster recovery from the ionizing event observed for the AISb/InAs HEMTs. Index Terms--AISb, charge collection, GaAs, HEMT, InAIAs, InAs, InGaAs, InP, MESFET, single-event transient, single-event upset.

Carrier generation based on subbandgap two-photon absorption is used to perform three-dimensional mapping of the single-event transient response of the LM124 operational amplifier. Three classes of single-event-induced transients are observed for the input transistor Q20. A combination of experiment and transistor level modeling is used to assign the different classes of measured transients to charge collection across specific junctions. The large-amplitude, positive-going transients cannot be assigned to a single junction, and are identified with a collector-substrate photocurrent. Index Terms--Analog single-event effects, laser-induced single-event effects, LM124 operational amplifier, nonlinear absorption, single-event transients.

Ultrafast electron dynamics are compared for small Au nanoparticles in two different surrounding environments. The relaxation time scale shows a weak dependence on excitation fluence but is essentially independent of the size of the Au nanoparticle embedded inside the dendrimer.

Carrier generation based on subbandgap two-photon absorption is demonstrated and shown to be a viable alternative to the conventional single-photon excitation approach in laser-induced single event effects. The two-photon approach exhibits characteristics distinct from those of single-photon excitation, and may be advantageous for a range of single-event effect investigations. The charge track produced by two-photon absorption more closely resembles that of heavy-ion irradiation and, because the photon energy is subbandgap, backside injection through bulk silicon wafers is straightforward and three-dimensional mapping is possible. Index Terms--Error injection, multi photon absorption, optical propagation in absorbing media, silicon, single-event effects, single-event transients, two-photon absorption.

Time-resolved charge-collection measurements are performed on InAIAs/InGaAs HEMTs with pulsed laser excitation as a function of device bias conditions and the incident laser pulse energy. The results provide clear evidence for the presence of charge-enhancement processes that, in many ways, are analogous to those observed previously for GaAs FET technology. Index Terms--HEMT, InAIAs, InAIAs/InGaAs, InGaAs, InP HEMT, SEU, single-event effects, single-event upset.

Time-resolved charge-collection measurements performed on AISb/InAs/GaSb resonant interband tunneling diodes (RITDs) with pulsed laser excitation exhibit complex behavior as a function of the device operating point. A model considering conventional charge-collection principles in combination with transient band-bending effects is proposed to describe the experimental results. In the proposed model, a transient distortion of the band structure of the device (transient band bending) induced by holes trapped in the GaSb valence band well modulates the dc current through the RITD. The manner in which this transient modulation is manifested in the experimental observable depends sensitively on the operating point of the device, giving rise to qualitatively different temporal signatures under different dc bias conditions. Index Terms--Charge collection, high electron mobility transistor (HEMT), monostable-bistable transition logic element (MOBILE), resonant interband tunneling diode (RITD), resonant tunneling diode (RTD), single-event effects (SEEs), single-event upset (SEU), transient band bending.

A study of an inhomogeneously broadened quantum-mechanical harmonic oscillator model of intermolecular nuclear coordinates is applied to the analysis of subpicosecond optical Kerr effect dynamics of neat CS2 and its binary solutions in alkane solvents is presented. The results show that for an inhomogeneously broadened distribution of oscillators, this model predicts the naturally the bimodal character of the subpicosecond OKE dynamics, a Gaussian-like ultrafast decay and a slower, quasi-exponential relaxation, that is universally observed in molecular liquids.