Inverse metal-assisted chemical etching of germanium with gold and hydrogen peroxide.

Metal-assisted chemical etching (MACE) is a flexible technique for texturing the surface of semiconductors. In this work, we study the spatial variation of the etch profile, the effect of angular orientation relative to the crystallographic planes, and the effect of doping type. We employ gold in direct contact with germanium as the metal catalyst, and dilute hydrogen peroxide solution as the chemical etchant. With this catalyst-etchant combination, we observe inverse-MACE, where the area directly under gold is not etched, but the neighboring, exposed germanium experiences enhanced etching. This enhancement in etching decays exponentially with the lateral distance from the gold structure. An empirical formula for the gold-enhanced etching depth as a function of lateral distance from the edge of the gold film is extracted from the experimentally measured etch profiles. The lateral range of enhanced etching is approximately 10-20µm and is independent of etchant concentration. At length scales beyond a few microns, the etching enhancement is independent of the orientation with respect to the germanium crystallographic planes. The etch rate as a function of etchant concentration follows a power law with exponent smaller than 1. The observed etch rates and profiles are independent of whether the germanium substrate is n-type, p-type, or nearly intrinsic.

Cost and benefit in the choice of ECT schedule. Twice versus three times weekly ECT.

BACKGROUND: We compared the antidepressant and cognitive effects of up to eight sessions of bilateral, brief pulse electroconvulsive therapy (ECT) administered twice (ECT x 2) or three times weekly (ECT x 3), to confirm that ECT x 3 acts more rapidly although the two schedules are equivalent in antidepressant outcome, and to establish whether ECT x 3 is indeed associated with more severe memory impairment. METHOD: Patients with major depression, endogenous subtype were randomly assigned to ECT x 3 or ECT x 2 plus one simulated ECT per week, both up to a maximum of eight real ECT. Depression was evaluated by the Hamilton Depression Scale the day after each treatment and cognitive function by a test battery administered before and after the ECT series and at one month follow-up. RESULTS: Assessed categorically or parametrically, there was no significant difference in antidepressant outcome between the two schedules. Rate of response was significantly more rapid with ECT x 3 but was associated with more severe memory impairment. CONCLUSIONS: Twice weekly administration is an optimum schedule for bilateral ECT unless clinical indications require the more rapid antidepressant effect of three times weekly treatment.

Electroconvulsive therapy and resistant depression: clinical implications of seizure threshold.

BACKGROUND: Patients with major depressive disorder (MDD) were treated with electroconvulsive therapy (ECT) to determine (1) variability of initial seizure threshold, (2) factors that influence seizure threshold, (3) change in seizure threshold during the ECT course, and (4) relationship of seizure threshold to antidepressant effects. METHOD: Seizure threshold was measured by a stimulus titration technique during the first, eighth, and final ECT of medication-free patients who had MDD, endogenous subtype based on Research Diagnostic Criteria and were randomly assigned to three-times-weekly, bilateral, brief pulse ECT (N = 24) or twice-weekly ECT plus one simulated treatment per week (N = 23). Subsequent to the first ECT, stimulus intensity was 1.3 to 1.8 (median = 1.5) times threshold. The Hamilton Rating Scale for Depression (HAM-D) was the primary clinical outcome measure. RESULTS: Initial seizure threshold varied by 594%. Gender (p = .03), total strength of pre-ECT pharmacotherapy trials (p = .02), and age (p = .12) accounted for 23.9% of the variance. Threshold increased by 42% +/- 26% (p = .0001) from the first to the final ECT, and seizure duration decreased by 33% +/- 28% (p = .0001). Seizure duration and mean stimulus intensity were negatively associated over all treatments (r = -.49, p = .0003). Change in HAM-D score was related to duration of the current depressive episode (r = -.39, p = .006) and total strength of pre-ECT pharmacotherapy trials (r = -.39, p = .008), but not to seizure threshold or duration. CONCLUSION: (1) Initial seizure threshold for pulse bilateral ECT is highly variable and not yet amenable to accurate prediction. (2) Stimulus titration allows threshold to be determined on an individual basis and dosage for subsequent treatments to be defined. (3) Seizure duration is of limited value as a sole criterion for the adequacy of treatment when initial threshold is unknown and/or electrical doses that substantially exceed threshold are used. (4) With moderately suprathreshold bilateral ECT, a relationship of seizure threshold to antidepressant response is not demonstrable.

Antidepressant and cognitive effects of twice- versus three-times-weekly ECT.

OBJECTIVE: The purpose of this study was to determine which of the two commonly used schedules of ECT administration, twice or three times weekly, is clinically optimal in terms of antidepressant efficacy and cognitive effects. METHOD: In this double-blind study, 52 consenting, medication-free patients with major depressive disorder, endogenous subtype (Research Diagnostic Criteria), were randomly assigned to bilateral, brief-pulse, constant-current ECT administered over 4 weeks at a rate of three times weekly or twice weekly with the addition of one simulated ECT (anesthesia and muscle relaxant only) per week. Outcome measures were the Hamilton Depression Rating Scale, Acute Cognitive Effects Battery, and Chronic Cognitive Effects Battery. RESULTS: Hamilton depression scale scores were significantly improved by both schedules, with no difference in outcome either 1 week or 1 month after the end of the ECT series. However, the rate of response to ECT three times a week was significantly faster and was related to the rate of real ECT administration. Cognitive effects were more prominent with ECT three times a week. CONCLUSIONS: ECT twice a week is an effective schedule for clinical practice and is potentially advantageous in view of a therapeutic outcome identical to that of ECT three times a week and less severe cognitive effects. ECT three times a week may be specifically indicated when early onset of clinical effect is of primary importance.